Add AppVeyor testing.

@giakki: things to do before merging

1. Add yourself an AppVeyor project and post the badge code so that I update the PR
2. Do we need coverage to be run here too?
3. Do we need node.js 0.11?

Example of how things will be https://ci.appveyor.com/project/XhmikosR/uncss

Keep in mind AppVeyor's cache isn't in effect since tests fail; when tests pass then it will be used.