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

src/Bullet3Common/b3HashMap.h

@@ -19,58 +19,6 @@ subject to the following restrictions:
 
 #include "b3AlignedObjectArray.h"
 
-///very basic hashable string implementation, compatible with b3HashMap
-struct b3HashString
-{
-	const char* 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) ||
-			(0==portableStringCompare(m_string,other.m_string));
-
-	}
-
-};
 
 const int B3_HASH_NULL=0xffffffff;