Bugfix and Enhancements

Feature: Add etc/ssl_dist.conf file for erlang SSL distribution (emq-relx#178)

Feature: Add node.ssl_dist_optfile option and etc/ssl_dist.conf file (#1512)

Feature: Support Erlang Distribution over TLS (#1512)

Improve: Tune off the 'tune_buffer' option for external MQTT connections (#1512)

emq-sn

Clean registered topics if mqtt-sn client send a 2nd CONNECT in connected state (#76)

Upgrade the esockd library to v5.2.1 (#76)

emq-auth-http

Remove 'password' param from ACL and superuser requests (#66)