Finished wall optimization, plus other things

- finished wall optimization
- boosted frame rate speed more
- changed the way "deleted" walls are drawn
- updated player graphic in the map creator
- added warp images -- floor and raised (ie like a 3D wall, but
transparent)
- various other small changes

I'll be drawing the warps on my next update, and also probably allowing
their (and multiple player spawns) placement in the map creator.