Consider adding SiteMap support to RSS connector

The RSS connector seems well suited for parsing sitemap XML and just doing the right thing. I'd propose adding the ability to parse sitemap XML in addition to parsing RSS and Atom. I would not go so far as automatically picking up the SiteMap field from robots.txt yet, however, since that would require another level of indirection that would need to be thought out. A direct reference in the "RSS URLs" field to the root sitemap URL would be where I'd start.

The Web connector should, of course, also get the ability to do this parsing, as it has for RSS feeds.