Also support a raw bytes message as well as the packet with src/dst headers #8

The Lora devices I communicate with don't use the packet structure that this has https://github.com/MZachmann/LightLora_MicroPython/blob/master/LightLora/lorautil.py#L6

So I'd like a way to also support this 'raw' message as well as the packet format. Would that be ok?