docs/qapidoc: implement transmogrify() method

docs/qapidoc: implement transmogrify() method

This is the true top-level processor for the new transmogrifier;
responsible both for generating the intermediate rST and then running
the nested parse on that generated document to produce the final
docutils tree that is then - very finally - postprocessed by sphinx for
final rendering to HTML &c.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-55-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
[Use the opportunity to move the __version__ assignment to where
PEP 8 wants it]
Signed-off-by: Markus Armbruster <armbru@redhat.com>