Support multiple values per key+issues

Because both the JSON and the ruby representation of WQL are hashes, we can't do multiple keys. This ends up limiting WQL in some important ways. We've implemented part of this ticket, so that you can write WQL to find all the cards that are either Cities or States.

But you can't yet find cards with "Katrina" or "Joseph" somewhere in the name, or are either tagged with "wiki" or have an image plussed to them.