Support moving nodes and refactor to eliminate recursion (#14)

* Refactor to eliminate recursion

* micro fix

* Added new `postOrderTraverse` method.

* style fix

* docs

* minor sonar fixes

* Make nodes movable; Rename `traverse` → `traverseInOrder`. Added new `traversePostOrder`.

* fix style

* minor fix

* Fixed tree movement - still constant time! (#15)

* - Return back to 4x ptr node footprint
- Introduced new "origin" fake node at tree.
- Fixed tree movement - still constant time!

* minor fix

* delete not in use constructor

* sonar fix