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diff --git a/vendor/tendril/src/fmt.rs b/vendor/tendril/src/fmt.rs
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+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Marker types for formats.
+//!
+//! This module defines the types and traits used to mark a `Tendril`
+//! with the format of data it contains. It includes those formats
+//! for which `Tendril` supports at least some operations without
+//! conversion.
+//!
+//! To convert a string tendril to/from a byte tendril in an arbitrary
+//! character encoding, see the `encode` and `decode` methods on
+//! `Tendril`.
+//!
+//! `Tendril` operations may become memory-unsafe if data invalid for
+//! the format sneaks in. For that reason, these traits require
+//! `unsafe impl`.
+
+use std::default::Default;
+use std::{char, mem, str};
+
+use futf::{self, Codepoint, Meaning};
+
+/// Implementation details.
+///
+/// You don't need these unless you are implementing
+/// a new format.
+pub mod imp {
+    use std::default::Default;
+    use std::{iter, mem, slice};
+
+    /// Describes how to fix up encodings when concatenating.
+    ///
+    /// We can drop characters on either side of the splice,
+    /// and insert up to 4 bytes in the middle.
+    pub struct Fixup {
+        pub drop_left: u32,
+        pub drop_right: u32,
+        pub insert_len: u32,
+        pub insert_bytes: [u8; 4],
+    }
+
+    impl Default for Fixup {
+        #[inline(always)]
+        fn default() -> Fixup {
+            Fixup {
+                drop_left: 0,
+                drop_right: 0,
+                insert_len: 0,
+                insert_bytes: [0; 4],
+            }
+        }
+    }
+
+    #[inline(always)]
+    unsafe fn from_u32_unchecked(n: u32) -> char {
+        mem::transmute(n)
+    }
+
+    pub struct SingleByteCharIndices<'a> {
+        inner: iter::Enumerate<slice::Iter<'a, u8>>,
+    }
+
+    impl<'a> Iterator for SingleByteCharIndices<'a> {
+        type Item = (usize, char);
+
+        #[inline]
+        fn next(&mut self) -> Option<(usize, char)> {
+            self.inner
+                .next()
+                .map(|(i, &b)| unsafe { (i, from_u32_unchecked(b as u32)) })
+        }
+    }
+
+    impl<'a> SingleByteCharIndices<'a> {
+        #[inline]
+        pub fn new(buf: &'a [u8]) -> SingleByteCharIndices<'a> {
+            SingleByteCharIndices {
+                inner: buf.iter().enumerate(),
+            }
+        }
+    }
+}
+
+/// Trait for format marker types.
+///
+/// The type implementing this trait is usually not instantiated.
+/// It's used with a phantom type parameter of `Tendril`.
+pub unsafe trait Format {
+    /// Check whether the buffer is valid for this format.
+    fn validate(buf: &[u8]) -> bool;
+
+    /// Check whether the buffer is valid for this format.
+    ///
+    /// You may assume the buffer is a prefix of a valid buffer.
+    #[inline]
+    fn validate_prefix(buf: &[u8]) -> bool {
+        <Self as Format>::validate(buf)
+    }
+
+    /// Check whether the buffer is valid for this format.
+    ///
+    /// You may assume the buffer is a suffix of a valid buffer.
+    #[inline]
+    fn validate_suffix(buf: &[u8]) -> bool {
+        <Self as Format>::validate(buf)
+    }
+
+    /// Check whether the buffer is valid for this format.
+    ///
+    /// You may assume the buffer is a contiguous subsequence
+    /// of a valid buffer, but not necessarily a prefix or
+    /// a suffix.
+    #[inline]
+    fn validate_subseq(buf: &[u8]) -> bool {
+        <Self as Format>::validate(buf)
+    }
+
+    /// Compute any fixup needed when concatenating buffers.
+    ///
+    /// The default is to do nothing.
+    ///
+    /// The function is `unsafe` because it may assume the input
+    /// buffers are already valid for the format. Also, no
+    /// bounds-checking is performed on the return value!
+    #[inline(always)]
+    unsafe fn fixup(_lhs: &[u8], _rhs: &[u8]) -> imp::Fixup {
+        Default::default()
+    }
+}
+
+/// Indicates that one format is a subset of another.
+///
+/// The subset format can be converted to the superset format
+/// for free.
+pub unsafe trait SubsetOf<Super>: Format
+where
+    Super: Format,
+{
+    /// Validate the *other* direction of conversion; check if
+    /// this buffer from the superset format conforms to the
+    /// subset format.
+    ///
+    /// The default calls `Self::validate`, but some conversions
+    /// may implement a check which is cheaper than validating
+    /// from scratch.
+    fn revalidate_subset(x: &[u8]) -> bool {
+        Self::validate(x)
+    }
+}
+
+/// Indicates a format which corresponds to a Rust slice type,
+/// representing exactly the same invariants.
+pub unsafe trait SliceFormat: Format + Sized {
+    type Slice: ?Sized + Slice;
+}
+
+/// Indicates a format which contains characters from Unicode
+/// (all of it, or some proper subset).
+pub unsafe trait CharFormat<'a>: Format {
+    /// Iterator for characters and their byte indices.
+    type Iter: Iterator<Item = (usize, char)>;
+
+    /// Iterate over the characters of the string and their byte
+    /// indices.
+    ///
+    /// You may assume the buffer is *already validated* for `Format`.
+    unsafe fn char_indices(buf: &'a [u8]) -> Self::Iter;
+
+    /// Encode the character as bytes and pass them to a continuation.
+    ///
+    /// Returns `Err(())` iff the character cannot be represented.
+    fn encode_char<F>(ch: char, cont: F) -> Result<(), ()>
+    where
+        F: FnOnce(&[u8]);
+}
+
+/// Indicates a Rust slice type that is represented in memory as bytes.
+pub unsafe trait Slice {
+    /// Access the raw bytes of the slice.
+    fn as_bytes(&self) -> &[u8];
+
+    /// Convert a byte slice to this kind of slice.
+    ///
+    /// You may assume the buffer is *already validated*
+    /// for `Format`.
+    unsafe fn from_bytes(x: &[u8]) -> &Self;
+
+    /// Convert a byte slice to this kind of slice.
+    ///
+    /// You may assume the buffer is *already validated*
+    /// for `Format`.
+    unsafe fn from_mut_bytes(x: &mut [u8]) -> &mut Self;
+}
+
+/// Marker type for uninterpreted bytes.
+///
+/// Validation will never fail for this format.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct Bytes;
+
+unsafe impl Format for Bytes {
+    #[inline(always)]
+    fn validate(_: &[u8]) -> bool {
+        true
+    }
+}
+
+unsafe impl SliceFormat for Bytes {
+    type Slice = [u8];
+}
+
+unsafe impl Slice for [u8] {
+    #[inline(always)]
+    fn as_bytes(&self) -> &[u8] {
+        self
+    }
+
+    #[inline(always)]
+    unsafe fn from_bytes(x: &[u8]) -> &[u8] {
+        x
+    }
+
+    #[inline(always)]
+    unsafe fn from_mut_bytes(x: &mut [u8]) -> &mut [u8] {
+        x
+    }
+}
+
+/// Marker type for ASCII text.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct ASCII;
+
+unsafe impl Format for ASCII {
+    #[inline]
+    fn validate(buf: &[u8]) -> bool {
+        buf.iter().all(|&n| n <= 127)
+    }
+
+    #[inline(always)]
+    fn validate_prefix(_: &[u8]) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn validate_suffix(_: &[u8]) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn validate_subseq(_: &[u8]) -> bool {
+        true
+    }
+}
+
+unsafe impl SubsetOf<UTF8> for ASCII {}
+unsafe impl SubsetOf<Latin1> for ASCII {}
+
+unsafe impl<'a> CharFormat<'a> for ASCII {
+    type Iter = imp::SingleByteCharIndices<'a>;
+
+    #[inline]
+    unsafe fn char_indices(buf: &'a [u8]) -> imp::SingleByteCharIndices<'a> {
+        imp::SingleByteCharIndices::new(buf)
+    }
+
+    #[inline]
+    fn encode_char<F>(ch: char, cont: F) -> Result<(), ()>
+    where
+        F: FnOnce(&[u8]),
+    {
+        let n = ch as u32;
+        if n > 0x7F {
+            return Err(());
+        }
+        cont(&[n as u8]);
+        Ok(())
+    }
+}
+
+/// Marker type for UTF-8 text.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct UTF8;
+
+unsafe impl Format for UTF8 {
+    #[inline]
+    fn validate(buf: &[u8]) -> bool {
+        str::from_utf8(buf).is_ok()
+    }
+
+    #[inline]
+    fn validate_prefix(buf: &[u8]) -> bool {
+        if buf.len() == 0 {
+            return true;
+        }
+        match futf::classify(buf, buf.len() - 1) {
+            Some(Codepoint {
+                meaning: Meaning::Whole(_),
+                ..
+            }) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    fn validate_suffix(buf: &[u8]) -> bool {
+        if buf.len() == 0 {
+            return true;
+        }
+        match futf::classify(buf, 0) {
+            Some(Codepoint {
+                meaning: Meaning::Whole(_),
+                ..
+            }) => true,
+            _ => false,
+        }
+    }
+
+    #[inline]
+    fn validate_subseq(buf: &[u8]) -> bool {
+        <Self as Format>::validate_prefix(buf) && <Self as Format>::validate_suffix(buf)
+    }
+}
+
+unsafe impl SubsetOf<WTF8> for UTF8 {}
+
+unsafe impl SliceFormat for UTF8 {
+    type Slice = str;
+}
+
+unsafe impl Slice for str {
+    #[inline(always)]
+    fn as_bytes(&self) -> &[u8] {
+        str::as_bytes(self)
+    }
+
+    #[inline(always)]
+    unsafe fn from_bytes(x: &[u8]) -> &str {
+        str::from_utf8_unchecked(x)
+    }
+
+    #[inline(always)]
+    unsafe fn from_mut_bytes(x: &mut [u8]) -> &mut str {
+        mem::transmute(x)
+    }
+}
+
+unsafe impl<'a> CharFormat<'a> for UTF8 {
+    type Iter = str::CharIndices<'a>;
+
+    #[inline]
+    unsafe fn char_indices(buf: &'a [u8]) -> str::CharIndices<'a> {
+        str::from_utf8_unchecked(buf).char_indices()
+    }
+
+    #[inline]
+    fn encode_char<F>(ch: char, cont: F) -> Result<(), ()>
+    where
+        F: FnOnce(&[u8]),
+    {
+        cont(ch.encode_utf8(&mut [0_u8; 4]).as_bytes());
+        Ok(())
+    }
+}
+
+/// Marker type for WTF-8 text.
+///
+/// See the [WTF-8 spec](https://simonsapin.github.io/wtf-8/).
+#[derive(Copy, Clone, Default, Debug)]
+pub struct WTF8;
+
+#[inline]
+fn wtf8_meaningful(m: Meaning) -> bool {
+    match m {
+        Meaning::Whole(_) | Meaning::LeadSurrogate(_) | Meaning::TrailSurrogate(_) => true,
+        _ => false,
+    }
+}
+
+unsafe impl Format for WTF8 {
+    #[inline]
+    fn validate(buf: &[u8]) -> bool {
+        let mut i = 0;
+        let mut prev_lead = false;
+        while i < buf.len() {
+            let codept = unwrap_or_return!(futf::classify(buf, i), false);
+            if !wtf8_meaningful(codept.meaning) {
+                return false;
+            }
+            i += codept.bytes.len();
+            prev_lead = match codept.meaning {
+                Meaning::TrailSurrogate(_) if prev_lead => return false,
+                Meaning::LeadSurrogate(_) => true,
+                _ => false,
+            };
+        }
+
+        true
+    }
+
+    #[inline]
+    fn validate_prefix(buf: &[u8]) -> bool {
+        if buf.len() == 0 {
+            return true;
+        }
+        match futf::classify(buf, buf.len() - 1) {
+            Some(c) => wtf8_meaningful(c.meaning),
+            _ => false,
+        }
+    }
+
+    #[inline]
+    fn validate_suffix(buf: &[u8]) -> bool {
+        if buf.len() == 0 {
+            return true;
+        }
+        match futf::classify(buf, 0) {
+            Some(c) => wtf8_meaningful(c.meaning),
+            _ => false,
+        }
+    }
+
+    #[inline]
+    fn validate_subseq(buf: &[u8]) -> bool {
+        <Self as Format>::validate_prefix(buf) && <Self as Format>::validate_suffix(buf)
+    }
+
+    #[inline]
+    unsafe fn fixup(lhs: &[u8], rhs: &[u8]) -> imp::Fixup {
+        const ERR: &'static str = "WTF8: internal error";
+
+        if lhs.len() >= 3 && rhs.len() >= 3 {
+            if let (
+                Some(Codepoint {
+                    meaning: Meaning::LeadSurrogate(hi),
+                    ..
+                }),
+                Some(Codepoint {
+                    meaning: Meaning::TrailSurrogate(lo),
+                    ..
+                }),
+            ) = (futf::classify(lhs, lhs.len() - 1), futf::classify(rhs, 0))
+            {
+                let mut fixup = imp::Fixup {
+                    drop_left: 3,
+                    drop_right: 3,
+                    insert_len: 0,
+                    insert_bytes: [0_u8; 4],
+                };
+
+                let n = 0x10000 + ((hi as u32) << 10) + (lo as u32);
+
+                let ch = char::from_u32(n).expect(ERR);
+                fixup.insert_len = ch.encode_utf8(&mut fixup.insert_bytes).len() as u32;
+
+                return fixup;
+            }
+        }
+
+        Default::default()
+    }
+}
+
+/// Marker type for the single-byte encoding of the first 256 Unicode codepoints.
+///
+/// This is IANA's "ISO-8859-1". It's ISO's "ISO 8859-1" with the addition of the
+/// C0 and C1 control characters from ECMA-48 / ISO 6429.
+///
+/// Not to be confused with WHATWG's "latin1" or "iso8859-1" labels (or the
+/// many other aliases), which actually stand for Windows-1252.
+#[derive(Copy, Clone, Default, Debug)]
+pub struct Latin1;
+
+unsafe impl Format for Latin1 {
+    #[inline(always)]
+    fn validate(_: &[u8]) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn validate_prefix(_: &[u8]) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn validate_suffix(_: &[u8]) -> bool {
+        true
+    }
+
+    #[inline(always)]
+    fn validate_subseq(_: &[u8]) -> bool {
+        true
+    }
+}
+
+unsafe impl<'a> CharFormat<'a> for Latin1 {
+    type Iter = imp::SingleByteCharIndices<'a>;
+
+    #[inline]
+    unsafe fn char_indices(buf: &'a [u8]) -> imp::SingleByteCharIndices<'a> {
+        imp::SingleByteCharIndices::new(buf)
+    }
+
+    #[inline]
+    fn encode_char<F>(ch: char, cont: F) -> Result<(), ()>
+    where
+        F: FnOnce(&[u8]),
+    {
+        let n = ch as u32;
+        if n > 0xFF {
+            return Err(());
+        }
+        cont(&[n as u8]);
+        Ok(())
+    }
+}