Miscellaneous documentation cleanups [v9_16]
Backport of MR !5752 (merged)
Commits with conversion from Markdown to reStructuredText were not backported but regenerated from v9.16 source files. The other commits were cherry-picked and hand-edited to match the source when needed, but generally polished texts from v9.19 were preferred over the original v9.16 texts.
Edited by Petr Špaček