Provide support for other games/generations

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I think this script could benefit from the functionality to load tiles from more games. I've been doing some basic reading, and the possibility is definitely there. From what I have seen, the DS games use a very different internal structure.

It would probably be beneficial to split the scripts up by game-- i.e. pokemap_gen3.py, etc. As of right now, I think any script that works in one game should work with games in the same generation/series (fire red and leaf green should both work with current version), but I'm not 100% sure on if that trend continues down the line.