Fixed the issue that invalid clients can publish will message. (emqttd#1230)
Fixed Dashboard showing no stats data (emqttd#1263)
Fixed a rare occurred building failure (emqttd#1284)
Support Persistence Logs for longer time (emqttd#1275)
Fix for users APIs (emqttd#1289)
Changed passwd_hash/2 function's return type (emqttd#1289)
Improved the Dashboard Interface of Monitoring/Management/Tools.
Allow switching dashboard themes.
Supoort both EN and CN languages.