Pass along attribute 'oldValues' to handlers.
Replace whitespace indentation by tabs.
Use prefixed WebKitMutationObserver if needed.
Implement 'exists' events.
fix: Properly check for added / removed nodes in mutation records.
Index handlers by ID instead of selector.
fix: Removal events didn't fire in some circumstances...

... Namely, when div.child was removed and should fire a handler for a selector such as '.parent .child'.
Implement 'handler-removed' event.
refactor: Always use underscored variable names.