plumb URDF/SDF audio_source into PhysicsServerCommandProcessor, allow to play sounds on collision !

See also https://youtu.be/eppOjTfx5Jg for a first test, and this modified URDF how to add sounds:
https://github.com/bulletphysics/bullet3/blob/master/data/plane_with_collision_audio.urdf
Add the --audio flag to enable sound in pybullet/Bullet-C-API

examples/Utils/b3HashString.h

@@ -0,0 +1,59 @@
+#ifndef B3_HASH_STRING_H
+#define B3_HASH_STRING_H
+
+#include <string>
+
+///very basic hashable string implementation, compatible with b3HashMap
+struct b3HashString
+{
+	std::string m_string;
+	unsigned int	m_hash;
+
+	B3_FORCE_INLINE	unsigned int getHash()const
+	{
+		return m_hash;
+	}
+
+
+	b3HashString(const char* name)
+		:m_string(name)
+	{
+
+		/* magic numbers from http://www.isthe.com/chongo/tech/comp/fnv/ */
+		static const unsigned int  InitialFNV = 2166136261u;
+		static const unsigned int FNVMultiple = 16777619u;
+
+		/* Fowler / Noll / Vo (FNV) Hash */
+		unsigned int hash = InitialFNV;
+		
+		for(int i = 0; m_string[i]; i++)
+		{
+			hash = hash ^ (m_string[i]);       /* xor  the low 8 bits */
+			hash = hash * FNVMultiple;  /* multiply by the magic number */
+		}
+		m_hash = hash;
+	}
+
+	int portableStringCompare(const char* src,	const char* dst) const
+	{
+			int ret = 0 ;
+
+			while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
+					++src, ++dst;
+
+			if ( ret < 0 )
+					ret = -1 ;
+			else if ( ret > 0 )
+					ret = 1 ;
+
+			return( ret );
+	}
+
+	bool equals(const b3HashString& other) const
+	{
+		return (m_string == other.m_string);
+	}
+
+};
+
+#endif //B3_HASH_STRING_H