CW decoder

This is an effort that took over a year to prepare and complete. I have tried several different methods for the CW decoder and I end up using the auto-correlation method. It seems that is more robust on low SNR values. However, it is a bit more CPU hungry, but RPI3 can handle it.

In addition, various CW debug blocks are also included, in case someone wants to play with the decoder or even use them for transmitting CW messages!