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 argument.

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.