wip merge pseudo-3d effect from broken-sign-games

[pancelor]

the code's a bit of a mess; it was never meant to last longer than the one game I made it for. but this is the basics of how I merged the 3d effect from https://github.com/broken-sign-games/PuzzleScript/ into PSP for my butter game

I don't intend for this to be merged as-is, and I don't currently have plans to work on it more. hopefully this will be a helpful starting point if you decide to take this up!