- Most of the shared code is in the HttpProtocol class (former Frame)
- Virtual calls handle protocol-specific things
- Move the ProcessRequestsAsync loop to HttpProtocol
- Implement HTTP/1.x request processing in Http1Connection and HTTP/2
in Http2Stream, with Http1Connection<T> and Http2Stream<T> subclassing
those classes in order to handle the generic HttpContext parameter
- Split MessageBody into Http1MessageBody and Http2MessageBody,
with MessageBody containing shared member variables and methods
