Misc documentation fixes.

- Misc grammar and punctuation fixes.

- Stylistic cleanup: use spaces between function arguments and JSON fields
  in examples. For example "foo(a,b)" -> "foo(a, b)". Add semicolon after
  last END in a few PL/pgSQL examples that were missing them.

- Make sentence that talked about "..." and ".." operators more clear,
  by avoiding to end the sentence with "..". That makes it look the same
  as "..."

- Fix syntax description for HAVING: HAVING conditions cannot be repeated

Patch by Justin Pryzby, per Yaroslav Schekin's report. Backpatch to all
supported versions, to the extent that the patch applies easily.

Discussion: https://www.postgresql.org/message-id/20201005191922.GE17626%40telsasoft.com

doc/src/sgml/high-availability.sgml

@@ -1502,7 +1502,7 @@ synchronous_standby_names = 'ANY 2 (s1, s2, s3)'
     Note that in this mode, the server will apply WAL one file at a
     time, so if you use the standby server for queries (see Hot Standby),
     there is a delay between an action in the primary and when the
-    action becomes visible in the standby, corresponding the time it takes
+    action becomes visible in the standby, corresponding to the time it takes
     to fill up the WAL file. <varname>archive_timeout</varname> can be used to make that delay
     shorter. Also note that you can't combine streaming replication with
     this method.