Starting work on doxygen cleanup. Many things still to be done.

doc/Doxyfile

doc/doxygen.main

intern/ghost/GHOST_C-api.h

intern/ghost/GHOST_ISystem.h

intern/ghost/intern/GHOST_C-api.cpp

source/blender/imbuf/IMB_imbuf.h

source/blender/imbuf/IMB_imbuf_types.h

source/blender/makesdna/DNA_action_types.h

source/blender/makesdna/DNA_actuator_types.h

source/blender/makesdna/DNA_customdata_types.h

source/blender/makesdna/DNA_documentation.h

source/blender/makesdna/intern/makesdna.c

source/blender/makesrna/RNA_access.h

source/blender/makesrna/RNA_define.h

source/blender/makesrna/RNA_enum_types.h

source/blender/makesrna/intern/makesrna.c

source/blender/makesrna/intern/rna_internal.h

source/blender/windowmanager/WM_api.h