Fix typos and grammar in documentation and code comments

Comment fixes are applied on HEAD, and documentation improvements are
applied on back-branches where needed.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20210408164008.GJ6592@telsasoft.com
Backpatch-through: 9.6

Author: michaelpq

doc/src/sgml/maintenance.sgml

@@ -185,7 +185,7 @@
     never issue <command>VACUUM FULL</command>.  In this approach, the idea
     is not to keep tables at their minimum size, but to maintain steady-state
     usage of disk space: each table occupies space equivalent to its
-    minimum size plus however much space gets used up between vacuumings.
+    minimum size plus however much space gets used up between vacuum runs.
     Although <command>VACUUM FULL</command> can be used to shrink a table back
     to its minimum size and return the disk space to the operating system,
     there is not much point in this if the table will just grow again in the

doc/src/sgml/ref/create_table.sgml

@@ -1488,7 +1488,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
     </listitem>
    </varlistentry>
 
-   <varlistentry id="reloption-autovacuum-vauum-scale-factor" xreflabel="autovacuum_vacuum_scale_factor">
+   <varlistentry id="reloption-autovacuum-vacuum-scale-factor" xreflabel="autovacuum_vacuum_scale_factor">
     <term><literal>autovacuum_vacuum_scale_factor</literal>, <literal>toast.autovacuum_vacuum_scale_factor</literal> (<type>floating point</type>)
     <indexterm>
      <primary><varname>autovacuum_vacuum_scale_factor</varname> </primary>
@@ -1578,7 +1578,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
     </listitem>
    </varlistentry>
 
-   <varlistentry id="reloption-autovacuum-vauum-cost-limit" xreflabel="autovacuum_vacuum_cost_limit">
+   <varlistentry id="reloption-autovacuum-vacuum-cost-limit" xreflabel="autovacuum_vacuum_cost_limit">
     <term><literal>autovacuum_vacuum_cost_limit</literal>, <literal>toast.autovacuum_vacuum_cost_limit</literal> (<type>integer</type>)
     <indexterm>
      <primary><varname>autovacuum_vacuum_cost_limit</varname></primary>

doc/src/sgml/ref/createuser.sgml

@@ -44,7 +44,7 @@ PostgreSQL documentation
    If you wish to create a new superuser, you must connect as a
    superuser, not merely with <literal>CREATEROLE</literal> privilege.
    Being a superuser implies the ability to bypass all access permission
-   checks within the database, so superuserdom should not be granted lightly.
+   checks within the database, so superuser access should not be granted lightly.
   </para>
 
   <para>