Feeds! Atom feeds for course-site items.

Feeds! Atom feeds for course-site items.

Some notes:

* all feeds are Atom; comments on my Atom details are welcome.

* several different feeds per course site. E.g., just top-level items;
  recently-changed items; a walk of all items in the site directory
  tree; many others possible.

* by design, the feeds themselves are anonymous-access. I don't see a
  real security risk here, but if exposing titles and modification
  dates violates some policy, we can change it.

* all links in the feeds refer back to the Reserves system, so they
  can be authenticated if necessary. This is also true for "URL items"
  -- the Atom link is back to the canonical item-URL in Reserves,
  which redirects to the target URL (if you're allowed to know it).

* Django has its own feed system. I tried it, and then chose not to
  use it. Genshi does a fine job, and IMHO Django makes it harder to
  offer multiple feed-variants on individual items like Courses. It
  looks good for simpler feed-needs though, and has the benefit of
  supporting both Atom and RSS. (Not that we couldn't do that with
  Genshi too.)

There's room for more feed types: "My Courses", "Things in My
Courses", "canned search", etc. Ideas are most welcome.

git-svn-id: svn://svn.open-ils.org/ILS-Contrib/servres/trunk@168 6d9bc8c9-1ec2-4278-b937-99fde70a366f