Header::parse_header() returns now a hyper Result instead of an option
this will enable more precise Error messages in the future, currently
most failures are reported as ::Error::Header.
BREAKING CHANGE: parse_header returns Result instead of Option, related
code did also change
The header is largely for internal use, however, it must be exported
because the header! macro uses it. As deref! is also a particularly
general name, this renames it to __hyper__deref! to prevent name
clashes.
BREAKING CHANGE: If you use deref! from the header module, you'll need
to switch to using __hyper__deref!.
It is no longer required, as we can use `<H as Header>::header_name()`.
BREAKING CHANGE: Implementations of Header will need to adjust the
header_name method. It no longer takes any arguments.
Currently headers are exported at many places. For example you can access
`Transfer-Encoding` header at `header`, `header::common` and
`header::common::transfer_encoding`. Per discussion on IRC with
@seanmonstar and @reem, all contents of headers will be exposed at `header`
directly. Parsing utilities will be exposed at `header::parsing`. Header
macros can now be used from other crates.
This breaks much code using headers. It should use everything it needs
directly from `header::`, encodings are exposed at `header::Encoding::`,
connection options are exposed at `header::ConnectionOption`.
