COMMENTS,POLISHING: comments fenzy around VisualProcessor machinery,

make process() a true interface as strong hint for derived classes,
plus misc define added for understanding.

BUGFIX: FFTDataDistributor loses incoming samples when compacting internal buffers.

BUGFIX2: FFTDistributor: Frozen Waterfall if internal buffer is no bigger than fftSize

src/demod/DemodDefs.h

@@ -59,6 +59,7 @@ class ModemKit;
 class DemodulatorThreadPostIQData: public ReferenceCounter {
 public:
     std::vector<liquid_float_complex> data;
+
     long long sampleRate;
     std::string modemName;
     std::string modemType;