* Use mongo_ruby_driver as much as possible
* Move mongoid dependency to a separate module
* Learn from other gems how they manage and support multiple adaptors
  - https://github.com/pluginaweek/state_machine/tree/master/lib/state_machine/integrations
  - https://github.com/ianwhite/orm_adapter
* Add support for mongo_mapper
* Add options hash validations
* Refactor specs