Implement InMemoryFile for memory caching for fileIO plugin.

Support SDF loading through fileIO plugin.
Replace strcspn by C code (not crossplatform)
Add flag for loadURDF to use color from MTL file (instead from URDF link material)
pybullet.URDF_USE_MATERIAL_COLORS_FROM_MTL and pybullet.URDF_USE_MATERIAL_TRANSPARANCY_FROM_MTL

examples/Importers/ImportMeshUtility/b3ImportMeshUtility.h

@@ -3,6 +3,12 @@
 
 #include <string>
 
+enum b3ImportMeshDataFlags
+{
+	B3_IMPORT_MESH_HAS_RGBA_COLOR=1,
+	B3_IMPORT_MESH_HAS_SPECULAR_COLOR=2,
+};
+
 struct b3ImportMeshData
 {
 	struct GLInstanceGraphicsShape* m_gfxShape;
@@ -11,6 +17,20 @@ struct b3ImportMeshData
 	bool m_isCached;
 	int m_textureWidth;
 	int m_textureHeight;
+	double m_rgbaColor[4];
+	double m_specularColor[4];
+	int m_flags;
+
+	b3ImportMeshData()
+		:m_gfxShape(0),
+		m_textureImage1(0),
+		m_isCached(false),
+		m_textureWidth(0),
+		m_textureHeight(0),
+		m_flags(0)
+	{
+	}
+
 };
 
 class b3ImportMeshUtility