Windows Travis Server

[jadamroth]

Now with the port to windows, we should create a windows CI server along with the existing linux travis server

[JohannesKauffmann]

There should definitely be a Windows CI server, preferably for both MSVC and MinGW. Maybe it would also be a good idea to add clang as a compiler to the current Linux setup.

Another important aspect of the CI is the ability to check every incoming PR, even those of forks. That way, if the CI runs the tests, no breakage should be able to go unnoticed. I know I broke the test once, and it was only fixed by someone else after my changes had been merged...

The current CI setup, however, hasn't ran for more than a year; it seems like Travis is not free anymore, and even open source projects will need to spend effort getting a finite amount of credits allocated [1].

I'd be happy to take a shot at getting GitHub Actions up and running, complete with the tests, whenever I have the time for it.

[1] https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing