- API Change: :destroy action now stores trackers in the format original=value, modified=nil (previously it was the reverse)

- Change to Tracker#affected which makes it behave more consistent with the previously released version (I had modified it in my other recent commits)

- Refactor complex method #history_tracker_attributes; create new private method #modified_attributes_for_action
- Fix bug related to memoization. In Trackable#track_update, there was a shortcut to return early which caused memoization not to be cleared properly in some cases (saw it in my app, not exactly sure how to reproduce)
- Cleanup / consolidate duplicate code
Add CodeClimate badge
Merge pull request #71 from johnnyshields/master

API change for :destroy action + memoization bugfix + CodeClimate badge