add soft-clipping of mixed sounds using tanh

expose ADSR to TinyAudio API
enable envelope when playing wav files

examples/TinyAudio/b3SoundEngine.h

@@ -2,6 +2,7 @@
 #define B3_SOUND_ENGINE_H
 
 #include "Bullet3Common/b3Scalar.h"
+#include "b3Sound_C_Api.h"
 
 struct b3SoundMessage
 {
@@ -11,10 +12,22 @@ struct b3SoundMessage
 	double m_frequency;
 	int m_wavId;
 
-	double m_attack;
-	double m_decay;
-	double m_sustain;
-	double m_release;
+	double m_attackRate;
+	double m_decayRate;
+	double m_sustainLevel;
+	double m_releaseRate;
+
+	b3SoundMessage()
+		:m_type(B3_SOUND_SOURCE_SINE_OSCILLATOR),
+		m_amplitude(0.5),
+		m_frequency(440),
+		m_wavId(-1),
+		m_attackRate(0.001),
+		m_decayRate(0.00001),
+		m_sustainLevel(0.5),
+		m_releaseRate(0.0005)
+	{
+	}
 };
 
 class b3SoundEngine