CI tests on Windows and macOS

[pombredanne]

It would be great to setup appveyor for Windows CI and add macOS CI on Travis

[jayfk]

Do you have expierence with appveyor? Set that up once, took me quite some time. Since you are a collaborator here, go ahead if you want to.

[deronnax]

Now these two can be done using GitHub Action. Is it still needed though?