Get the build process working on OSX

[Ameobea]

Since I do most of my development on mac these days, it will be very helpful to be able to build and run the platform on it. In addition, many people use mac and being able to have it install there without having to go through extra hassle is a great bonus.

In the future, I'd like to get it building on Windows as well, but as I don't really have a way to test that (and it's not a priority for me right now) that will have to wait for another time.