Add AppVeyor testing for Windows

Things we need before merging

- [ ] Someone should add JSHint in AppVeyor themselves and should post the badge code so that I update the patch.
- [ ] Enable cache for the npm modules; this requires the build to pass first, see #1931 too.

Example https://ci.appveyor.com/project/XhmikosR/jshint/build/1.0.12
This project doesn't use Grunt, so the Grunt CLI isn't necessary.