Test on Mac and Windows

[ralphtheninja]

I think we should enable 'osx' on Travis and also add AppVeyor for windows. Mostly because level is the "main" module.

[ralphtheninja]

We should also remove the compiler things in .travis.yml for faster tests (prebuilt binaries should be available).

[ralphtheninja]

@vweevers Add to Projects if you agree.

[ralphtheninja]

OSX done here #111