GNU Radio Block for SDRPlay for APIv3

First try to let a GNU Radio block cooperate with the SDRPlay version 3 API. Already plays FM radio on a constant frequency, so still needs work to get all the parameter passing going: Frequency, Gain, ...

Implemented a CW to digital decder block in C++. Is a rectifier using abs(), followed by mean of last n values (Resistor Capacitor).

• Analog output to watch the result
• Schmitt-Trigger output for digital post processing
• Message output issuing a time message in sample count every time a signal rise or fall is detected. Least significant bit indicate rise or fall.

Picks up messages indcating signal state changes and their timing. Timings are collectes on a circular lerning buffer, one buffer for "on"-lenghts, the other one for "off"-lengths. At regular intervals the kMeans cluster algorithm calculates the dot and the dash clusters for the on-vector as well as the signal-gap, letter-gap and word-gap for the off-vector. The calculated timings are used for decode timing.

ToDo: Handle long pauses in transmissions as well as long carrier signals.