Setup continuous integration and testing

[balthisar]

I know that a lot of PR's have gone stale because I've generally not been available since my daughter's birth. Sorry about that.

We're still interested in multiplatform testing before merging PR's, which is where things are falling apart. It looks like GitHub Actions now have some built-in continuous integration and continuous testing features in the last year or so available, and it looks like it supports Windows, Linux, and macOS.

I've done some initial playing with it, and I can get it to build on Ubuntu and macOS targets with success. I think I could get it to pull from our testing repository, and run regressing tests every time a PR is made. This would tell us right away that all tests pass on the various platforms.

The obvious benefit is that no one has to wait for me to test on macOS or Linux before a PR is merged.

I'll assign this to myself for the time being, and perhaps I'll have some time to work on it in the next week.

Comments, please! If there's no interest, I won't bother.

Please note: I'm still not back full-time, but I'll do what I can.

[balthisar]

I've learnt a bit about Github actions, and have come up with a working C.I. solution on private fork of the repository.

It works well, and builds Tidy on four platforms, and runs through all of the regression testing automatically. There's probably a lot more that it can do, such as release our binaries automatically, but I think this is an excellent start.

When giving some thought to pull requests, though, we really want them to be accompanied by test cases as well, and it would be convenient to do this in a single PR, rather than a PR for Tidy and a PR for the test case. I'm not kidding when I say that this would allow us to judge PR's in a few minutes rather than waiting for folks to test on our own timeline on multiple platforms.

Our test cases used to be present in the main repository, and I propose merging them back into the main repository once again.

I may merge in the C.I. solution as is as a demo, but re-unifying the repositories would be a better step.

Thoughts?

[balthisar]

Lacking any discussion, I've merged in the automated testing. As a result, I've been able to test and approve several PR's today.