feat(lib): add support to disable tokio-proto internals

For now, this adds `client::Config::no_proto`, `server::Http::no_proto`,
and `server::Server::no_proto` to skip tokio-proto implementations, and
use an internal dispatch system instead.

`Http::no_proto` is similar to `Http::bind_connection`, but returns a
`Connection` that is a `Future` to drive HTTP with the provided service.
Any errors prior to parsing a request, and after delivering a response
(but before flush the response body) will be returned from this future.

See #1342 for more.

src/proto/body.rs

@@ -7,6 +7,7 @@ use std::borrow::Cow;
 use super::Chunk;
 
 pub type TokioBody = tokio_proto::streaming::Body<Chunk, ::Error>;
+pub type BodySender = mpsc::Sender<Result<Chunk, ::Error>>;
 
 /// A `Stream` for `Chunk`s used in requests and responses.
 #[must_use = "streams do nothing unless polled"]