feat: add automatic GitHub issue comment links

[onerandomusername]

depends on #227, GH-227

[shiftinv]

Other fragment types I've seen, that aren't being handled yet:

• Linking to PR comments from file view: https://github.com/onerandomusername/monty-python/pull/234/files/886b69691a644741c0dad0743744a957ebbdabc6#r1150000416
  • This doesn't necessarily have a commit hash, files#r12341234 is also possible
• Seems like older PR comments (< mid 2016) use #discussion-diff- instead of pullrequestreview-, e.g. python/asyncio#355 (diff)
  • The link doesn't actually seem to fully work anymore in the gh UI, but the api docs still reference that fragment format
• Linking to the first message of an issue or PR: #228 (comment)

[onerandomusername]

Other fragment types I've seen, that aren't being handled yet:

* Linking to PR comments from file view: [onerandomusername/monty-python/pull/234/files/886b69691a644741c0dad0743744a957ebbdabc6#r1150000416](https://github.com/onerandomusername/monty-python/pull/234/files/886b69691a644741c0dad0743744a957ebbdabc6#r1150000416)
  
  * This doesn't necessarily have a commit hash, `files#r12341234` is also possible

Given the additional handling this requires on /files/ urls I personally don't want to implement this at the moment, but I wouldn't deny a pr to add it.

* Seems like older PR comments (< mid 2016) use `#discussion-diff-` instead of `pullrequestreview-`, e.g. [Ensure get_event_loop returns the running loop when called in a coroutine python/asyncio#355 (diff)](https://github.com/python/asyncio/pull/355#discussion-diff-65616522)
  
  * The link doesn't actually seem to fully work anymore in the gh UI, but the api docs still reference that fragment format

I can't recreate this, sorry.

* Linking to the first message of an issue or PR: [feat: add automatic GitHub issue comment links #228 (comment)](https://github.com/onerandomusername/monty-python/pull/228#issue-1634393638)

Changed...