Patch review req: make assert_routing handle HTTP methods

At present, fully testing your resourceful routes is a pest because
assert_routing doesn't like anything other than a string as it's first

Well, no longer! The patch I just attached to fixes up assert_routing to properly
handle hashes in it's first argument, so it works more like
assert_recognizes. It has tests *and* documentation. It's, like, the
perfect patch.

+1s appreciated.

- Matt

Looks clean.