Large code/documentation cleanup

[baronkobama]

Summary

This PR does a ton of things, but I'll attempt to summarize here:

• Fixes a large amount of spelling and grammatical errors in code (not entirely necessary, but it removes linting typo/proofreading errors).
• Fixes broken links on documentation (not all fixed, see below for remaining).
• Polishes redundant code -- a few examples:
  • Remove _Undefined in favor of MISSING in abc.py.
  • Remove unused imports in several files.
  • Edit tuple returns to return val, val, ... instead of (val, val, ...).
• Shortens lines that extend past L120.
• Fixes some small bugs.
• More small things I am probably glossing over.

Regarding broken links, there are still a few that remain and I have yet to get around to fixing yet. Namely:

• Auto mod objects (i.e. AutoModRule, AutoModActionExecutionEvent, and more) that are referenced in the documentation (here and here from what I've found) are broken links as the objects are not currently listed anywhere in the documentation. (will be handled in a separate PR)
• Any references to ForumChannel in the documentation are broken as it is not currently listed anywhere. (found here, here, here, here, and here so far.)
• Not all members of TextChannel are being displayed on the docs, resulting in missing attributes on the object itself and a broken reference. (broken reference found here, haven't found any others so far.)

Also, lastly, this PR will probably remain in draft until the broken links listed above are fixed (any help is much appreciated, I can't do much more documentation work for my own sanity) and the changes made here are ensured to not cause any issues (once again, any testing done is much appreciated).

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting, examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.

[Lulalaby]

Please don't say this should go into release too 😅

[Lulalaby]

tbh LGTM so far, @Dorukyum what you think

[EmmmaTech]

Shortens lines that extend past L120.

Personally I think instead that another Black linting PR (that re-adds the CI with some differences) would be better for this instead of doing it in this PR.

[baronkobama]

Personally I think instead that another Black linting PR (that re-adds the CI with some differences) would be better for this instead of doing it in this PR.

Should this be done? I don't see a reason to undo those changes just so it can be done again, but if others think so then I can revert them.

[Lulalaby]

I meant only featureable ^^
GitHub mobile sucks

I read your whole pr in bed because I couldn't sleep XD

Meow

[Lulalaby]

Again I'm sleepy and once more I approve this pr as LGTM.
And because I only fixed a merge conflict YEEEEEEEEET

[Middledot]

Otherwise lgtm