===================
- **BREAKING** Requires Python 2.7 or 3.4+. Closes 163.
- **BREAKING** Remove support for SSL without SSLContext (Requires Python 2.7.9+ or 3.2+).
Closes 115.
- **BREAKING** on_connect callback is now always called flags. Previously this
callback could accepts 3 OR 4 arguments, now it must accepts 4. Closes 197.
- **BREAKING** tls_insecure_set() must now be called *after* tls_set()
- Allow username and password to be zero length (as opposed to not being
present). Closes 80.
- Allow zero length client ids when using MQTT v3.1.1.
- Add SSLContext support, including SNI. Closes 11.
- Improved support for unicode topic and binary payload.
Closes 15, 16.
- Allow arbitrary Websocket headers and path.
Closes 169.
- Fix issue with large inbound payload over Websocket. Closes 107.
- Add exponential delay for reconnection. Closes 195.
- Move unit tests to pytest (164) and tox (187)
- Add support for standard Python logging. Closes 95.
- Fix duplicate incoming QoS==2 message. Closes 194.