Add support for 20.1.0.3, 20.3.0.3, 20.3.0.6 nif formats.

include/NIF_IO.h

include/gen/AVObject.h

include/gen/ControllerLink.h

include/gen/Header.h

include/gen/Morph.h

include/gen/TexDesc.h

include/gen/TexSource.h

include/nif_basic_types.h

include/nif_versions.h

include/obj/NiControllerSequence.h

include/obj/NiExtraData.h

include/obj/NiFloatExtraDataController.h

include/obj/NiGeometry.h

include/obj/NiGeometryData.h

include/obj/NiImage.h

include/obj/NiObjectNET.h

include/obj/NiPSysModifier.h

include/obj/NiPSysModifierCtlr.h

include/obj/NiSequence.h

include/obj/NiSourceTexture.h