message: feat(header): add Encoding::Brotli variant
  BREAKING CHANGE: This adds a new variant to the `Encoding` enum, which
  can break exhaustive matches.
diff: use std::fmt;
  use std::str;
  -pub use self::Encoding::{Chunked, Gzip, Deflate, Compress, Identity, EncodingExt};
  +pub use self::Encoding::{Chunked, Brotli, Gzip, Deflate, Compress, Identity, EncodingExt};
  /// A value to represent an encoding used in `Transfer-Encoding`
  /// or `Accept-Encoding` header.
  @@ -9,6 +9,8 @@ pub use self::Encoding::{Chunked, Gzip, Deflate, Compress, Identity, EncodingExt
  pub enum Encoding {
  /// The `chunked` encoding.
  Chunked,
  + /// The `br` encoding.
  + Brotli,
  /// The `gzip` encoding.
  Gzip,
  /// The `deflate` encoding.
  @@ -25,6 +27,7 @@ impl fmt::Display for Encoding {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  f.write_str(match *self {
  Chunked => "chunked",
  + Brotli => "br",
  Gzip => "gzip",
  Deflate => "deflate",
  Compress => "compress",
  @@ -39,6 +42,7 @@ impl str::FromStr for Encoding {
  fn from_str(s: &str) -> ::Result<Encoding> {
  match s {
  "chunked" => Ok(Chunked),
  + "br" => Ok(Brotli),
  "deflate" => Ok(Deflate),
  "gzip" => Ok(Gzip),
  "compress" => Ok(Compress),
  