An API for using MQTT over multiple transports

Dependencies:   FP MQTTPacket

Dependents:   Cellular_HelloMQTT IoTStarterKit GSwifiInterface_HelloMQTT IBMIoTClientEthernetExample ... more

Issue: Unsubstribe from topic doesn't kill callback

Whenever a topic is unsubsribed successfully and subsribed afterwards again, there are two call backs alive that recieve messages ... unfortunately the first (initial) callback function is not shutdown and is still actively recieving messages ... which means that two callbacks are fired whenever a message is recieved