NanoMQ v0.8.2 更新日志

This is a bug-fix release for 0.8.0

1. New packaging method for taking packages.io as the default installation.
2. Refactoring HTTP REST APIs to be compatible with EMQX.
3. Remove CXX compiler requirement
4. Rule engine now supports parsing JSON payloads.
5. Fix Nanolib's compatibility with GCC under 4.9 #634
6. Fix data racing of issue #666
7. Fix MQTT over Websocket # 668
8. Fix disconnect msg does not cleanup last will msg.