PyBullet: added preliminary DART and MuJoCo backend files, MuJoCo can loadMJCF, stepSimulation and getBasePositionAndOrientation, DART is empty.

PyBullet: add 2d biped example.,

examples/SharedMemory/dart/DARTPhysicsC_API.h

@@ -0,0 +1,20 @@
+#ifndef DART_PHYSICS_C_API_H
+#define DART_PHYSICS_C_API_H
+
+#ifdef BT_ENABLE_DART
+
+#include "../PhysicsClientC_API.h"
+
+#ifdef __cplusplus
+extern "C" { 
+#endif
+
+//think more about naming. The b3ConnectPhysicsLoopback
+B3_SHARED_API	b3PhysicsClientHandle b3ConnectPhysicsDART();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //BT_ENABLE_DART
+#endif //DART_PHYSICS_C_API_H