Access-Control-Allow-Origin origins are URLs but they do not need to
be valid, they should just be compared as strings. So to support
invalid URLs hyper should use a string instead.
closes#526
BREAKING CHANGE: Access-Control-Allow-Origin does no longer use Url
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 spec says the header can be either a `*`, `null` or an URL.
Improve docs of header.
BREAKING CHANGE: Add variant to Access-Control-Allow-Origin enum
This is the last bunch of headers that should use the new macro. Moved them out of
their own folder so that the macro works. Changed them, so that they are more in
line with the other headers.
BREAKING CHANGE: `AccessControlAllowHeaders` and `AccessControlRequestHeaders` values
are case insensitive now. `AccessControlAllowOrigin` variants are now `Any` and
`Value` to match the other headers.
