Feature: issue#262 - Add 'http://host:8083/mqtt/status' page for health check
Bugfix: issue#271 - add emqttd_ws_client:subscribe/2 function
Bugfix: issue#269 - bin/emqttd Syntax error on ubuntu
Bugfix: issue#259 - when clustered the emqttd_dashboard port is close, and the 'emqttd' application cannot stop normally.
Improve: issue#265 - client under unstable mobile network generate a lot of logs
Improve: issue#257 - After the node name changed, the broker cannot restart for mnesia schema error.