Support for Collection Helpers

I found [Collection Helpers](https://github.com/dburles/meteor-collection-helpers) very useful to generate derived attributes for collections.

If this package could support matching fields of derived attributes, it would be very neat. I don't quite understand internally how this works, but by intuition it seems to be not very hard.

Thanks for the hard work of the project maintainer.

No files, tests, or entry points are named. First identify how collection fields are matched, then define a reproducible example using a derived attribute and add coverage for matching it.

Written by the indexing model from the issue text.