Adds send_message helper. (#484)
Adds send_message helper. (#484)

* Adds a helper function similar to send_event that sends an arbitrary OpenLCB
message to the bus using synchronous allocation.
bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn