revmoing sdl2_gfx headers, build update
	modified:   .travis.yml
	modified:   CMakeLists.txt
	deleted:    StiGame/SDL2_framerate.h
	deleted:    StiGame/SDL2_gfxPrimitives.h
	deleted:    StiGame/SDL2_gfxPrimitives_font.h
	deleted:    StiGame/SDL2_imageFilter.h
	deleted:    StiGame/SDL2_rotozoom.h