WIP. send a large constant string twice a second, in order to test out the transport with something indicative of our required load.

Dependencies:   FXOS8700CQ NTPClient azure_umqtt_c iothub_mqtt_transport mbed-rtos mbed wolfSSL Socket lwip-eth lwip-sys lwip

Fork of FXOS8700CQ_To_Azure_IoT by Mark Radbourne