* WIP
* Bugs
* Enhancements
** Automated tests
*** Long packets, short packets
** TLS
*** Client certificate and key
** Offline buffering
*** Queue outbound publishes in progress and retry with dup=1 after reconnect.
** Client connect sends clean session
** Client connect sends last will
** Local persistent buffering
** High availablity: fail over to a list of servers on failure to connect
** MQTT over WebSocket
** Back pressure on write PID allocation?
At the moment we just return an error.
** Publish QoS level 2 (exactly once)
** Subscribe QoS level 2 (exactly once)