Give DirtySet and Tracker common event listener methods
Bump version to 0.0.3
Merge pull request #5 from doredesign/common_event_listener

Give DirtySet and Tracker common event listener methods
Restore Tracker#on_event for backwards compat
Merge pull request #6 from doredesign/common_event_listener

Restore Tracker#on_event for backwards compat