Improve composability of collection argument matchers

* Makes array_including able to take matchers as part of its expected argument
* Makes array_including describe passed matchers so that descriptions compose correctly
* Makes hash_including describe passed matchers so that descriptions compose correctly.
It would be nice to include a failing example as well.  As this currently exists, `array_including` could be written to always match when passed a matcher argument, and all the specs would pass.