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.
Unfortunately, currently :program: doesn't link to the program's page.
So we use the old-school :ref: again where we should link, i.e. for
everything that's not the program the current page is about.
Fixes#8438
