Removed CONTINATION frame.  Added reset state.

Removed the priority fields from META_DATA (aka HEADERS) as they can always
be sent as a separate PRIORITY frame.  META_DATA is now just the same as
CONTINUATION, so there is no need for CONTINUATION.

Changed the END_STREAM semantics so that it is always set on the last frame.

Improved RESET handling so that there is a "reset" state and that RST_STREAM
messages are achnowledged.  This allows closed to really be closed!