merge *dat.h, *fns.h; rewrite and port more funs

- c3_draw: FixedByFrac: yet to be simplified and tested
- c3_game: GameLoop
- c3_main: rewrite, port
- c3_scale: DeplanePic
- id_in: stub INL_GetMouseButtons, INL_GetJoyButtons, IN_GetJoyButtonsDB,
  IN_AckBack, IN_Ack
don't use intptr_t like an idiot
port/rewrite rest of c3_game

asm untested.
move files around a bit to make more manageable

u -> unused