Check links are correct and fix those that aren't

[adetaylor]

Fixes #957

[mgeisler]

Thanks @adetaylor! I rebased this on top of main and there are a few new errors — in addition to the ones in the translations.

You could update the translations yourself, we could disable checking links there, or perhaps some other approach?

Testing this out it's nice: it caches the results and won't slow down the build (or mdbook serve).

[adetaylor]

You could update the translations yourself, we could disable checking links there, or perhaps some other approach?

It actually looked to be a little fiddly to update the translations, since it appears that they do link to pages which may (or may not) actually exist when your browser is set to a different language. I think it possibly does need the actual translators to go through the mistakes.

I'm not quite sure what to do here. Disabling the link checking for translations seems bad, but perhaps as an interim step we should do that?

[randomPoison]

@adetaylor I'm in favor of disabling broken link checking for translations 👍 At least ensuring that the link is correct in the original English is an improvement of the current situation, and we can continue to fix broken links in the translations manually until we can figure out how to automatically valid links in translations.

Can you rebase this onto main and update it to only check the English slides?