* Improved Singly Linked List
Added String Representations of Nodes and Linked Lists
Added support for indexing and changing of Node data using indices.
* Added a few comments to Linked Lists
* Reformatted to conform to PEP8
* Added from_sequence.py
Convert a Python List to Linked List comprising of Nodes and return head.
* Added print_reverse.py
Recursive program to print the elements of a Linked List in reverse.
* Change 'is not None' for more Pythonicness
