Adds associated `Body` and `BodyError` types to `IntoResponse`. This is required for returning responses with bodies other than `hyper::Body` from handlers. That wasn't previously possible.
This is a breaking change so should be shipped in 0.2.
This breaks up `extract.rs` into several smaller submodules. The public
API remains the same.
This is done in prep for adding more tests to extractors which would get
messy if they were all in the same file.