elmo-rss.el

This is a trivial to use RSS/Atom/OPML backend for Wanderlust.  Unlike shimbun, it requires no configuration — just point it at a suitable feed, and it will do everything automatically:

    rss:https://github.com/wanderlust/wanderlust/commits/master.atom

It should handle all known feed types (two variants of Atom, three variants of RSS) except for binary-only Atom feeds.

Since it's a new backend, it shouldn't break anything.  I'm finding this extremely useful for tracking github/gitlab commits, and would appreciate if it could be merged.

@ikazuhiro, perhaps you could add Japanese documentation?

--jch