[x] Every map has an exit table
[x] Tiles that are flagged as exit have all the rest of their flags point into the exit table
[ ] Exits may be locked
+[ ] Add sprite based door animation that plays while the map is doing a prtial redraw
[x] Doors may be opened and can unveil more of the map
[x] Implement partial map redraws. Allow queueing up a map redraw which then is processed over several frames. Allow setting a start address, tiles per row and rows to redraw.