docs: Use :doc: role when linking to commands

This makes it so we link to the very top of the document instead of a
special anchor we manually include.

So clicking e.g. :doc:`string <cmds/string>` will link you to
cmds/string.html instead of cmds/string.html#cmd-string.

I would love to have a way to say "this document from the root of the
document path", but that doesn't appear to work, I tried
`/cmds/string`.

So we'll just have to use cmds/string in normal documents and plain
`string` from other commands.

doc_src/cmds/commandline.rst

@@ -29,7 +29,7 @@ The following options are available:
 **-f** or **--function**
     Causes any additional arguments to be interpreted as input functions, and puts them into the queue, so that they will be read before any additional actual key presses are.
     This option cannot be combined with any other option.
-    See :ref:`bind <cmd-bind>` for a list of input functions.
+    See :doc:`bind <bind>` for a list of input functions.
 
 **-h** or **--help**
     Displays help about using this command.