only push denormalize_to changes if the field is dirty
Merge remote-tracking branch 'icambron/save_on_dirty' into feature/only_change_when_dirty
- Improved https://github.com/logandk/mongoid_denormalize/pull/12 based on code review comments.
- Assorted other code style improvements.
- Added information about :as option to the README, plus info about getting started with jeweler.
Merge pull request #15 from rehevkor5/feature/only_change_when_dirty

only push denormalize_to changes if the field is dirty (improved)