Refactor DoublyLinked.__init__() and Node.__init__() by removing default arguments and explicitly setting attributes so that all lists are instantiated empty and all nodes are instantiated without association to a list. This forces use in an expected manner and reduces the potential for unforseen problems for an end user.
Refactor DoublyLinked() and Node() to be more pythonic and readable.
Update test_doubly_linked.py to account for changes made to attribute names in DoublyLinked() and Node()
Update DoublyLinked() and Node() docstring formatting to better conform to PEP 257
Merge pull request #18 from jefrailey/doubly_linked

Doubly linked