RTTY FSK - Nanoio code integration

[Olivier-ADLER]

With the remaining program memory we have using a Mega 2560 AVR (around 60 % free), and because K3NG is fully modular, it should be possible to integrate FSK support for keyboard sending as well as NanoIO for FSK emulation.

Decoding is probably possible too with a 16 MHz clock.

This would give a better utilization of the power of those quite powerful processors and would avoid to have a second device for FSK.