Connection: transforming TODO list into GitHub tickets.
Stream: documenting the public API.
Stream: emitting and error when receiving an invalid frame.
Connection: adding section stub for API documentation.
Stream tests: expect stream to emit error events when error happens.
Stream tests: improving how outgoing frames are checked.
Flow: new base class for doing flow control.
Stream: using Flow as base class for flow control.
Stream: updating state machine to handle WINDOW_UPDATE and PRIORITY more liberally. Fixes #18.