Fix more typos and inconsistencies in documentation

Fix more typos and inconsistencies in documentation

This fixes a couple of grammar mistakes, typos and inconsistencies in
the documentation.  Particularly, the configuration parsing allows only
"kB" to mean kilobyte but there were references in the docs to "KB".
Some instances of the latter are still in the code comments.  Some
parameter values were mentioned with "Minus-one", and using directly
"-1" with proper markups is more helpful to the reader.

Some of these have been pointed out by Justin, and some others are
things I bumped into.

Author: Justin Pryzby, Michael Paquier
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/20190330224333.GQ5815@telsasoft.com