Feature: Passed org.eclipse.paho.mqtt.testing/interoperability tests
Feature: Qos0, Qos1 and Qos2 publish and suscribe
Feature: session(clean_sess=false) management and offline messages
Feature: redeliver awaiting puback/pubrec messages(doc: Chapter 4.4)
Feature: retain messages, add emqtt_server module
Feature: MQTT 3.1.1 null client_id support
Bugfix: keepalive timeout to send will message
Improve: overlapping subscription support
Improve: add emqtt_packet:dump to dump packets
Test: passed org.eclipse.paho.mqtt.testing/interoperability
Test: simple cluster test
Closed Issues: #22, #24, #27, #28, #29, #30, #31, #32, #33, #34, #36, #37, #38, #39, #41, #42, #43