Added Collection::listNested()
Implemented the 3 iterator modes for listNested
Documenting new function
Added a not explaining how to use the TreeIterator constants instead
Documenting new classes
Added test for using a callable in listNested
Started to implement a tree printer method
Adding test for the tree printer
Added some docs
Documenting more functions
Added test for TreeIterator
Fixed CS issue
Fixed typos
Using integer instead of int
Merge pull request #3257 from cakephp/3.0-tree-iterator

3.0 tree iterator