Setup CI
Add a CI so that pull requests can be verified to build, and maybe eventually pass tests.
Looks like we have GitHub Actions access now, so I should try that.
Also, CI should do builds using the various -fsanitize runtimes, like thread, address, and undefined.
I was going to set it up with Azure, but I guess GitHub actions is the future. Unfortunately I don't have access yet :-(
I was originally thinking of Azure too. I haven't used either of the two, so I'm not sold on one vs the other. I agree that Actions seems like the way of the future, but it's yet to be seen how either of them handle a build that depends on swift.