include docs over binary protocol

Currently, the include_docs=true parameter pulls in content over HTTP. It's less optimized and less performant than pulling the same content via a get_multi() request.

However, get_multi() is currently broken over the binary protocol.

This commit shows some progress on the API design:
http://review.couchbase.org/#/c/20349/

That would allow the developer to make a request like:
users = cb['default']['_design/game']['users_by_points'].results().docs()

and get back the content of each user's document, regardless of it being a JSON doc or not.

Currently, that code is broken and the implementation is knowingly bad due to having to work around the current lack of .get_multi() on CouchbaseClient and the brokenness of .get_multi() on the MemcachedClient. The current code in that commit returns only the last document requested in the list of results.