Moving the `pluck` and `ids` methods to their own delegate line.

The two methods `pluck` and `ids` aren't really statistical helper methods and don't belong in the group of delegators that they currently are stuck in. In my opinion, they also don't really belong in any other group which is being delegated for querying, so I'm moving them to their own group of methods.

I've also changed the `:to => :all` hash syntax to `to: :all`.