[Query] Support matching references with $in

[jmikola]

The references() and includesReferenceTo() builder methods, which are for ReferenceOne and ReferenceMany, respectively, only support a single document as their argument. We should have helper methods to match against multiple referenced documents (using $in). This is trivial for simple references, as it would simply use $in, but it requires something more complex for DBRef references (see: here).

This issue was prompted by: http://stackoverflow.com/a/28304608/162228

[stale]

This issue has been automatically marked as stale because it has not had any recent activity. It will be closed in a week if no further activity occurs. Thank you for your contributions.