This commit also changes the signature of the 'ContentType'
'from_extension" method so that it returns an 'Option<ContentType>' as
opposed to 'ContentType'.
This commit also disallows negative quality values in 'Accept' media
types.
Differential and causal profiling determined that 35% of `Hello, world!`
dispatch time was spent rendering `Content-Type` due to many calls to `fmt` in
`MediaType::Display` and an allocation in `ContentType::Into<Header>`. This
change reduces the number of calls to `fmt` to 1 in `MediaType::Display` and
removes the allocation in `Into<Header>` for known media types.
This change also caches a `Rocket` "precheck" so that pre-dispatch checks are
done only a single time for a given `Rocket` instance, further reducing
`MockRequest::dispatch_with` time for "Hello, world!" by roughly 15%.
This is a breaking change.
This commit changes the meaning of the `format` route attribute when
used on non-payload carrying requests (GET, HEAD, CONNECT, TRACE, and
OPTIONS) so that it matches against the preferred media type in the
`Accept` header of the request. The preferred media type is computed
according to the HTTP 1.1 RFC, barring a few specificty rules to come.
Sergio Benitez