Generate mutation records where appropriate.
Add common base class for non-node clients.
Add basic mutation observer infrastructure.
Implement observer registration and record queues.
Implement async callbacks for mutation observers.
Add more mutation observer tests and a few bugfixes.
Add main file for library users.
Allow subclassing Document and Element clients.
Allow callback to return false to abort iteration.
Fix undefined nodeIndex variable.
Prevent extra lookup.
Fix invalid previousSibling when inserting a node at the same place.
Fix issues with tracking registered observers for a given target.