An assert is now raised if iterator operations are called before an iterator is assigned to a list, closes #21. Refractored the List::Insert() method so that it has the same structure as List::Delete(), closes #13. Added unit tests that delete nodes from the start and the end of lists, as well as many from the middle, closes #12. Added operator overload for addition of Iterator and integer so we can increment/decrement more than one node at a time, closes #6.