Export functionality

I'm starting to work on making exporting happen. Not at all ready to merge - I'm just curious what you think.
When ```runMode.SketchType==SCRIPT```, the getLibraryDir function doesn't care what the path to the sketch is (that argument), it only uses the path to the running .jar file.
It's a fragile API but I wasn't sure what else to do here. I could dig up a path somewhere but it wouldn't get used.