PROTON-696: Remove pn_buffer_t and pn_frame_t from the public API
(they are currently only used privately)
- Don't want to expose a potentially changing internal detail
- XXX Currently left the DLL exports in because of proton and proton-dump
PROTON-769: Move trace flags entirely to transport code
PROTON-770: Change dispatcher interface (more parameters for frame handlers)
- Use transport, frametype and channel
- Pass more of the frame directly into the frame handlers
PROTON-771: Validate performative against frame type
PROTON-770: Eliminate pn_dispatcher_t:
- Moved all useful state from pn_dispatcher_t to pn_transport_t
- Only left input frame dispatching in dispatcher.[ch]