Setup AppVeyor

[jdknives]

Feature description

We are in the process of simplifying builds for Windows. Once that has been completed we should run the test suite and build steps we are currently running on Travis for Linux and MacOS on Windows as well. Travis does not support Windows.

We should check AppVeyor since it should

• support Windows, Linux and MacOS
• otherwise seems to have the same features and similar pricing

As discussed on Matrix, we should also check the possibility of building our releases on AppVeyor.

Is your feature request related to a problem? Please describe.

We currently do not run tests or builds on Windows.

Describe the solution you'd like

Preferably we would run tests and builds (potentially release builds) on one single platform against all three OS.

Describe alternatives you've considered
We could stay on Travis and just run Windows builds on AppVeyor, which would require us using and subscribing to two separate platforms.