docs: fix inconsistencies in markup and case

docs: fix inconsistencies in markup and case

Ensure to properly mark up function parameters in text with <parameter>,
avoid using <acronym> for terms which aren't acronyms and properly place
the ", and" in a value list. The acronym removal is a follow-up to commit
fb72a7b8c3 which removed it for minmax-multi.  In passing, also fix an
incorrectly cased word.

Author: Ekaterina Kiryanova <e.kiryanova@postgrespro.ru>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/c050ecbc-80b2-b360-3c1d-9fe6a6a11bb5@postgrespro.ru
Backpatch-through: v14