Add machine-readable dates to keep docs up-to-date

[camelid]

Is there someway to make the data references machine parseable? We could then write a simple tool to remind us when references are ~6 months old, and we should check it they’re still true.

Originally posted by @rylev in #1013 (comment)

[camelid]

I suggested one way of doing it here: #1013 (comment)

Another way is to use HTML comments like <!-- date: 2021-01-10 -->, which seems very feasible. Then we can add those comments to parts of the docs that say "As of now" or "As of January 2021" and then we can have a GitHub Action that automatically creates an issue after 6 months saying "Check in on this spot".

[jyn514]

We decided in today's meeting that we should do this with a GitHub action that runs monthly and opens at most one issue with checkboxes for each section of the guide that's out of date (and preferably tag it with E-easy).

[camelid]

Status update:

I've been working on this, and I think it's almost done! 🎉
I'm not familiar with GitHub Actions beyond basic cargo build CI, so I
think I'm going to test it on a private repo first to make sure it works.

I also had an idea for a way to make sure people use <!-- date: 2021-01 -->:
We add another GitHub Action as part of CI that looks for the phrase as of now
(case-insensitive and with varying whitespace of course) and fails CI if it
finds one. It then prints out a message to the logs or, better yet, posts a
comment that says something like:

Please use the phrase as of January 2021 instead of as of now since it
makes it easier to determine if something is still true. Additionally,
please add a <!-- date: 2021-01 --> comment near the as of January 2021
phrase so that our automated system can pick it up. Thanks!

where January 2021 and 2021-01 would be whatever the current month was.
I think this check could be implemented fairly easily. Maybe I can do it after I
finish the date-checker.

[rylev]

@camelid FYI: we're currently using TravisCI though there is an issue for switching to GitHub Actions #940

[camelid]

Yeah, I think it's better if new things are added to GitHub — plus it's easier since it seems GitHub Actions would have better integrations with GitHub, e.g. for opening issues ;)

[camelid]

I tested this on a private repo, and confirmed that it works! 🎉

PR: #1037

[camelid]

Since it's February 3, and thus we missed the start of the month, and also to test it, I'm going to manually trigger a run of the date-checker now!

[camelid]

It worked! #1046