Update {} to Unit, and some small changes

This library no longer compiles with the current Prelude, which uses Unit instead of {}. This fixes this. It also adds the output directory to .gitignore, and changes the .purs.hs to .purs, making the library easier to use with a build tool. If it bothers you having these all in one pull request, I can seperate them, but I figure that they are small and uncontroversial changes.