Add support for Mongoid

[kylejw2]

Mongoid works very similar to ActiveRecord. I have an application with relationships between ActiveRecord models and Mongoid models. When an ActiveRecord model (with Mongoid models belonging to it) is cloned, I'd like to have the Mongoid models cloned as well.

[moiristo]

I've never used Mongoid myself, but the reflection on associations is probably a lot different? As I don't have any experience with it I won't be adding this, but PR's are welcome :) You could use the pre/postprocessor or block option to include these associations for now.