Linux Build

I've not actually used Linux since University, but in theory Unity has native support for it. A user asked me if I would mind supporting it, and offered to help play-test it. As with the OSX version, you'll need to chmod to add execution permissions (Windows doesn't have anything like that, and so Unity can't apply it), but apart from that it appears to work out of the box.

Let me know if there's any problems; me debugging it will be a little bit like a blind man trying to solve a puzzle, but I'll try my best :)