Add automatic generation of a todo item page

Add automatic generation of a todo item page

This adds a script to generate the todo item page from
bugzilla. This requires a valid username+password for
bugzilla, so it is intended that this only be run on
the libvirt.org website via cron. Normal usage will just
generate an empty stub page.

* docs/todo.pl: Script to extract todo items from bugzilla
* docs/todo.cfg-example: Example config file
* docs/sitemap.html.in: Add todo page
* docs/Makefile.am: Generation rules for todo items