Upload tarballs with every release

[chiphogg]

This is to give users a stable archive whose SHA they can depend on. GitHub does not guarantee stability of the SHA over time for automatically generated archives. (Remember when they broke the world last January?)

The "righteous" thing to do here is that every time you cut a release, you should upload a .tar.gz archive and attach it to the release. Here's an example of a release that has an artifact like this: besides the two auto-generated ones, there's also au-0.3.4.tar.gz, whose contents are stable and will never change. Here's the section of our own release instructions that show how to obtain the .tar.gz file easily.

[f0rmiga]

Thank you. I haven't made any releases since it changed homes. I'll do one later today.

[chiphogg]

By the way, I see that there have been a couple of new releases, but they didn't include a manually uploaded stable tarball. Do you have a release checklist that you follow? If so, that might be a good place to add that step.