update default parameters + python updates

- by default ggwave will now output 32-bit float samples
- python samples no longer use numpy
- python test now decodes payload
- fix buffer overflow in receive.py example

src/ggwave.cpp

@@ -268,7 +268,7 @@ const GGWave::Parameters & GGWave::getDefaultParameters() {
         GGWave::kBaseSampleRate,
         GGWave::kDefaultSamplesPerFrame,
         GGWAVE_SAMPLE_FORMAT_F32,
-        GGWAVE_SAMPLE_FORMAT_I16
+        GGWAVE_SAMPLE_FORMAT_F32,
     };
 
     return result;