docs/string: Separate "pad" and "shorten"

This isn't the same as "join"/"join0", where one is just a special
case of the other.

These are two different, if basically opposite commands.

But more importantly this was a huge mess and the formatting was broken.

doc_src/cmds/string-pad.rst

@@ -48,13 +48,13 @@ Examples
     >_ string pad -w$COLUMNS (date)
     # Prints the current time on the right edge of the screen.
 
-
+.. END EXAMPLES
 
 See Also
 --------
 
+.. BEGIN SEEALSO
+
 - The :doc:`printf <printf>` command can do simple padding, for example ``printf %10s\n`` works like ``string pad -w10``.
 
 - :doc:`string length <string-length>` with the ``--visible`` option can be used to show what fish thinks the width is.
-
-.. END EXAMPLES

doc_src/cmds/string-shorten.rst

@@ -81,13 +81,15 @@ Examples
     # Taking 20 columns from the right instead:
     …in-path-with-expand
 
+.. END EXAMPLES
+
 See Also
 --------
 
+.. BEGIN SEEALSO
+
 - :ref:`string<cmd-string>`'s ``pad`` subcommand does the inverse of this command, adding padding to a specific width instead.
   
 - The :doc:`printf <printf>` command can do simple padding, for example ``printf %10s\n`` works like ``string pad -w10``.
 
 - :doc:`string length <string-length>` with the ``--visible`` option can be used to show what fish thinks the width is.
-
-.. END EXAMPLES

doc_src/cmds/string.rst

@@ -154,8 +154,8 @@ Examples
    :start-after: BEGIN EXAMPLES
    :end-before: END EXAMPLES
 
-"pad" and "shorten" subcommands
----------------------------------
+"pad" subcommand
+----------------
 
 .. include:: string-pad.rst
    :start-after: BEGIN SYNOPSIS
@@ -165,10 +165,22 @@ Examples
    :start-after: BEGIN DESCRIPTION
    :end-before: END DESCRIPTION
 
+Examples
+^^^^^^^^
+
 .. include:: string-pad.rst
    :start-after: BEGIN EXAMPLES
    :end-before: END EXAMPLES
 
+See also
+^^^^^^^^
+
+.. include:: string-pad.rst
+   :start-after: BEGIN SEEALSO
+
+"shorten" subcommand
+--------------------
+
 .. include:: string-shorten.rst
    :start-after: BEGIN SYNOPSIS
    :end-before: END SYNOPSIS
@@ -177,10 +189,19 @@ Examples
    :start-after: BEGIN DESCRIPTION
    :end-before: END DESCRIPTION
 
+Examples
+^^^^^^^^
+
 .. include:: string-shorten.rst
    :start-after: BEGIN EXAMPLES
    :end-before: END EXAMPLES
 
+See also
+^^^^^^^^
+
+.. include:: string-shorten.rst
+   :start-after: BEGIN SEEALSO
+
 "repeat" subcommand
 -------------------