Fix sphinx strictness-related failures

This was caused by #2399 CI invocation happening before
merging PR #2427 that made Sphinx nitpicky.

This change corrects the typo introduced by #2426.

Group development related files together

Add Python 3.9 trove classifier to the metadata

GHA: Replace 3.9 beta with 3.9 final

Link to build_meta documentation

Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

Fix ReST syntax error in the PEP 517 link

docs: code-block style fix

docs: editorial word fix

Report test results in the AppVeyor UI

📝 Enable showing news categories in towncrier log

Resurrect docs interlinking

🔥 Get rid of the unused sphinx `Makefile`

Fixes #2424

It's been lost as a part of https://github.com/pypa/setuptools/pull/2097

ignore any exception when loading 2to3

Make an illustrative change notes guide in GH UI