Blinking stars implemented

The next beta will have blinking stars.

I think I wrote a pretty neat implementation, involving separate palette entries for each star and a pair of identical Galois LFSRs running 1/4 cycle out of phase. Basically one LFSR iterates randomly through the stars turning them off, and the other follows 1/4 cycle behind turning them back on. 4 stars gets turned off and 4 stars get turned on every VBLANK interrupt. Looks good enough!

Blinking aside, in theory the implementation has the same number of stars, with the same colours, and the same distribution as the original. I may have messed up the Neo Geo tile orientation and/or sprite tile ordering as I can visually confirm it's identical, but it's close enough.