Port CI to Github Actions

[stefanv]

We don't have enough Travis-CI credits to make this work, so will switch over to GA.

[mattip]

If you have to choose, I would say working on moving multi-build/multibuild is more critical. A CI run here is about 30 minutes on linux. The multibuild one is about 10 hours on macOS (32 runs of 20 minutes), which is equivalent to 50 hours of linux time, and another couple of hours on linux. We have over 20,000 credits, which would last quite a while for the repo alone but will be gone in a flash on multibuild.

[stefanv]

Ah, woops, let me switch the issue over to that repo.

[stefanv]

Two issues that came up:

• GA only supports ubuntu 18.04 and 20.04, not xenial and trusty as currently used
• GA does not support other architectures out of the box. I can make these targets run under qemu, perhaps, but not confident of how well that will work.

@matthew-brett I will probably need a bit more context about what this action does to help out here.

[matthew-brett]

No problem for switching to 18.04 and 20.04.

By other architectures - do you mean all XCode / macOS variants? No - these will have to go - and be restricted to the options in https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners

Can you say more about the context that you need? I couldn't immediately work out what you meant.

[mattip]

See also #434. It seems this repo now has only appveyor integration, which seems also broken :(

@stefanv, I think at this point anything to move us forward would be welcome. For now only x86_64, we can deal with aarch64, ppc64le, s390x and arm64 later.

[mattip]

I created a test.yml basic action that can be modified to run macos, windows, linux testing for x86_64.

[cclauss]

#429 is now green on AppVeyor Python 3.7 only but it is a start...

[mattip]

I think this can be closed?