Python decoder example

This version incorporates the "omni.c" decoder for rtl_433 that will be incorporated into the mainstream rtl_433 repository. It is functionally the same as the earlier versions but complies with coding standards.

This version also includes Omni00.py as a model for end-consumer decoding of "fmt=0" (channel 0) messages from the microcontroller. That "pass-through" approach avoids the need to modify the "omni.c" decoder on your rtl_433 server but allows you to decode your microcontroller messages directly on the end-consumer system.