* refactor the framer to pack both control and STREAM frames
* refactor framer STREAM frame packing logic
* pack STREAM_DATA_BLOCKED in the same packet as the STREAM frame
This makes debugging easier (and is slightly more efficient). In the
pathological case where there is not enough space remaning in the packet
to pack the STREAM_DATA_BLOCKED frame, it is queued for the next packet.
* add an integration test