Enable Windows CI testing using AppVeyor.

This sets up AppVeyor to test SunPy using miniconda. JP2 cannot be tested because openJEPG is not a conda package (we could make one) and ANA still has that windows bug, so these tests are skipped.

Currently the testing matrix is smaller, only Numpy 1.8.1 and 1.7.1 on Python 2.7 is tested, it is not possible to build sphinx due to other dependencies like TeX and GraphViz.

AppVeyor integrates with GH like Travis does, unfortunately the GH API only shows the most recently reported event as the status of a commit / PR. I can find no way to disable the reporting from AppVeyor, the only possible solution is only to run the windows tests on master and manually check them every now and then.