Ladders now have proper open-space shafts. Their sprite has been edited to remove the faux-hole, and also the down sprite is now at the same vertical pixel adjustment as the up sprite, so it looks kinda like they connect.
For security's sake, you can no longer fall down an openspace if there is a ladder on the openspace tile. Strangelly enough there was already code for not falling down if there was a ladder below you.
Added flight to some simple mobs that had been excluded from Alberyk's initial runthrough (parrots, bees, bats, and shades.)
The purpose of this PR is that you can now fly up ladder shafts.
6f3fa4eba9