Add Azure Pipelines for automated tests

[pmetzger]

Travis is very unreliable for CI testing these days, and it's likely to get worse as they've lost a lot of staff. The MacPorts project has been very successfully using Azure Pipelines for the last few months as a secondary test system; it almost never has spurious failures. It would be good for us to set the same thing up for ocaml-community.

[c-cube]

I'm also wondering about github actions, as they're baked in (although still in beta)?

[pmetzger]

Both might be a fine thing! I think it's important that we slowly phase out Travis though.

[c-cube]

revisiting that, github actions are more robust these days, aren't they?

[pmetzger]

They are.

[UnixJunkie]

Travis is also very brittle and forces people to spend significant time maintaining a working CI test suite...

[mjambon]

As mentioned in another thread, my experience with GitHub Actions has been bad and I don't see how it could ever be fixed. On the other hand, CircleCI has been working perfectly.