A few last minute changes.. I think this will be all.

Run topic contents through html.markup.  That makes ref:, pep:, and html: links if they exist.  (I meant to this earlier.)

Fix case where topic reference links are to objects rather than another topic.  (applies to keywords also.)

Skips making an empty reference section if there are no references with a topic.

These are all small changes, and nothing should be controversial in this as everything changed only effects the new html browser mode.