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.
- Some stray deriving -> derive changes
- use::{mod} -> use::{self}
- fmt.write -> fmt.write_str
This does not catch the last case of fmt.write_str in the
Show impl of a Header Item. This will need to be changed
separately.
Instead, you can use an instance of a NetworkConnector with
`Request::with_connector`. This allows overloading of the NetworkStream
constructors, so that it is easy to modify how an `HttpStream` is
created, while still relying on the rest of the stream implementation.
BREAKING CHANGE
