PEP 685: Copyedit and fix various minor issues following further changes

[CAM-Gerlach]

Clarifications:

• Refine description of PEP 503 substitution to avoid implying that only the substitution character (-) is replaced or that only collapsing is done, and slightly expand examples.
• Add that a critical distinction between safe_extra() and PEP 503 is normalizing non-PEP 508 characters, avoid implying that only collapsing (as opposed to both collapsing and replacement) is not done for - and ., and briefly mention the further inconsistency with the function's docstring.
• Tweak discussion of PyPI results to explicitly make clear that potential "clashes" were global, not project-specifc
• Clarify what specifically was being followed in Setuptools and that a key factor in going with PEP 503 instead was a lack of real-world backward compat issues

Copyedits:

• Fix some grammar issues
• Add clarifying verbiage in a handful of places
• Avoid repetition in a few places
• Use more appropriate diction in a couple spots

Fixes:

• Add a few missing commas
• Add verbatim around a few appropriate elements
• Use inline links per PEP 12 and clean Discourse URLs
• Update Post-History per new PEP 12 guidance
• Remove empty Open Issues section

[brettcannon]

@CAM-Gerlach just to make sure there's no confusion, I'm letting you merge this since it's your PR. 🙂

[CAM-Gerlach]

@brettcannon I was letting you merge it because it was your PEP...heh.

In all seriousness, sorry about that; I can be too conservative about merging things sometimes, especially on this repo.

I reverted the other change you requested and will wait for the current issue with GitHub Actions/webhooks/pages/etc. to be resolved before merging, since when I merged a PR on another repo a short while ago, the GHP deploy never kicked off and the site didn't update, and I see that the builds on this PR pushing just now didn't trigger either.

[brettcannon]

In all seriousness, sorry about that; I can be too conservative about merging things sometimes, especially on this repo.

NP! If you didn't have commit rights I would have merged it, but since you do I prefer not to do the merge as you might have last-minute tweaks to do (see the miscommunication Jelle and I had I think last month).

[CAM-Gerlach]

NP! If you didn't have commit rights I would have merged it, but since you do I prefer not to do the merge as you might have last-minute tweaks to do (see the miscommunication Jelle and I had I think last month).

No, I totally understand—I was there for that, and I've seen that happen on other PRs here and elsewhere as its easy for there to be a miscommunication. If I'm doing knarly stuff like a rebase or critical changes I'll temporarily mark it as draft to prevent an inadvertent merge, but its a pretty heavy-handed tool to use for a lot of common cases, so that makes sense. Anyway, without further ado...