As per the GBATEK docs. Fixes the fadeout animations in Ice Age.
Former-commit-id: 0bc54ab594ba19347a4b6d1b681ccf37da4d7910
Former-commit-id: 33b732e7f990c312bf92bcc21797df35b3d2ce56
Writing to reference point BGnX and BGnY should update the internal PPU
registers also inside VBLANK period.
fixes#79
Former-commit-id: a5237319ccab1aab023bb05878c81a198310fb21
Former-commit-id: 0c9ce4476111eea46e7372b48af77c862c0d2f6a