Javadoc changes
Replaced 'matt' with 'Matt Champion'
Renamed 'TreeWalkers' and 'TreeIterators' to 'TreeWalkerFactory' and 'TreeIteratorFactory' to be more consistent with the selectors.
Moved the builder factory methods out of Trees and into a new class, TreeBuilderFactory
Renamed 'Trees' methods for obtaining factories to be consistent and more terse
Cache the factory objects and builder objects