Adaptor for TouchDB and CouchDB

This pull request includes a few additional tests as well.

To run the tests against the TouchDB / CouchDB adapter, see the note in `docs/tests.md`

There's a small test server and its npm dependencies in the `util/` directory. Probably simpler to include the dependencies then to ask people to run `npm install`

I also tested the adapter by running a demo app with it, the new tests cover behavior the app depended on that wasn't tested. Here's the demo app I used https://github.com/jchris/lawnchair_notes