Added more list exceptions to highlight oddball corner cases
Fixed oddball corner cases

...by raising an exception, EmptyListError, when pop() and top() are used on an empty list. Also, those functions operate correctly on corner cases len=0 and len=1.
fix: insert() and push() were returning type LinkedList.Node

 and  now return type LinkedList and the calling list
add unit testing compatible with python 2.7
Merge branch 'master' of https://github.com/iamrekcah/cs-fundamentals