Add windows CI build

[bpmweel]

As a Satsense developer
I would like to add a windows build to the automated build system
so that I can be sure that satsense works correctly on windows systems

Windows on appveyor (Boatswain has appeveyor config as an example)

[bouweandela]

It looks like Travis is also starting to support windows:
https://blog.travis-ci.com/2018-10-11-windows-early-release

[bouweandela]

Example appveyor configuration file that uses conda and looks pretty close to what we need (if we decide to use conda):
https://github.com/pytroll/satpy/blob/master/appveyor.yml