BGE Clean-up: New EXP prefix for the BGE Expression module

The expression module now uses an EXP prefix and it follows a
distribution similar to blender.

Additionally the hash function in EXP_HashedPtr.h was simplified and the
files EXP_C-Api.h &.EXP_C-Api.cpp were deleted because were unused.

Reviewers: campbellbarton, moguri, sybren, hg1

Projects: #game_engine

Differential Revision: https://developer.blender.org/D1221

source/gameengine/GameLogic/SCA_PythonController.cpp

@@ -39,7 +39,7 @@
 #include "SCA_LogicManager.h"
 #include "SCA_ISensor.h"
 #include "SCA_IActuator.h"
-#include "PyObjectPlus.h"
+#include "EXP_PyObjectPlus.h"
 
 #ifdef WITH_PYTHON
 #include "compile.h"