New features:

• Iterators extended:
  • Begin() for iterators to reset iterator (one-before-first).
  • End() for iterators to move iterator past the end (one-past-the-end).
  • First() for iterators to jump to first element.
  • Last() for reversible iterators to jump to last element.

Fixes and Improvements:

• RebBlackTree iterator to be explicit about its state

#20