add meetings feed

I've added the meetings feed only yet. Can you have a look and if you are happy with it, I will add the rest too.
Just realised that this isn't going to be ordered by anything other than the on disk order, but having them in published_at order would be better.  Have a look at the ``ChildrenQuery`` object in ``lrug_helpers`` and wrap the ``sitemap.where(:slug => 'meetings').first`` call in that, then you should be able to use the ``order_by`` call to make sure the articles are in order (and also do a where(:status => 'Published') to make sure we don't expose drafts).