Simplified the choice between len and cbp receive

Implemented radio.c/radio_get_payload ...

Not yet tested

Framework for FSK receive in place

Tested with MiHome adaptor plus, new FSK transmitter works fine

FSK Transmit coded, ready for test

Tested on Raspberry Pi, switch, monitor, and legacy work with spi scaffold

radio2.py offers temporary spi interface for radio.py ...

Tested on mac only.

Improved configurability of message repeat patterns. ...

Tested with different repeat lengths.
Optimum seems to be 8 inner, 1 outer transmits

Tested with learning mode. ...

Works with all 4 switch patterns.
Can now independently switch 4 switches.
Some occasional RF reliability problems that need measuring.

Improved flow of code, specifically radio_transmit() ...

Pushes previous mode and restores at end of transmit.
This should auto-return to standby or receive as appropriate.
This will make it easier to implement mode hopping schemes later.

Simulation gets further now due to gpio_sim detection

radio_rpi.so now built as part of the pi build process ...

legacy.py now uses the prebuilt radio_rpi.so

Tested radio2.py on Raspberry Pi, now works with OOK transmit

radio2.py ctypes wrapper ready for testing

Preparations for new radio interface added to the architecture