Change the three modules(Presence, Retainer, Subscription) to standalone plugins:

emq_mod_retainer: Retained Message Storage emq_mod_presence: Publish presence message to $SYS topics when client connected or disconnected emq_mod_subscription: Subscribe topics automatically when client connected

Update the SSL certificates under the etc/certs/ folder.

Bugfix: Fixed a typo (#716)

Bugfix: emqttd_http can not use emq_auth_http? #739

Bugfix: emq_auth_redis cannot use hostname as server address (#741)

Upgrade Redis, MySQL, Postgre and MongoDB plugins to support hostname.