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