#92 Support "tagging" multiple sections and topics

[Joe Stewart]

Allow multiple topics and sections to be specified in
the url by separating with "+" character.

One use would be to maintain a hierarchy.

Also could be used to have more free form tagging
linking the site in different ways similar to
del.icio.us tags (http://del.icio.us/doc/about).

Parsing the url to genererate the query shouldn't
require too much change. Whether to support quicker
creation of new topics and sections is another.