Tidy up outdated cruft in repo?

[purcell]

I suspect we don't make tarball releases any more, and that a lot of the cruft in the repo could be tidied up? I'd be quite keen to add a small Github Actions configuration here at some point in order to test byte compilation and maybe run package-lint over things.

[dgutov]

If you have the time, go for it. :-)

I haven't looked into using Github Actions anywhere yet.

We also have a few tests now, those could also be set up to run.

[snogge]

I've cleaned up the autoconf/automake stuff and added Github Actions to run the tests in #133.
package-lintremaining.