Fix and improve several places in the docs

Michael Paquier <michael@paquier.xyz>

Commit: 170d11b8e7cb9df96a7ee0b8140d28536d55fe3e
Author: Michael Paquier <michael@paquier.xyz>
Date: 2019-07-13T05:43:29Z
Releases: 13.0
Fix and improve several places in the docs

This adds some missing markups, fixes a couple of incorrect ones and
clarifies some documentation in various places.

Author: Liudmila Mantrova
Discussion: https://postgr.es/m/a068f947-7a51-5df1-b3fd-1a131ae5c044@postgrespro.ru
Backpatch-through: 12

Files

Documentation touched

Discussion