Dubley linkedlist

Here we implement a doubly link with quite a rich set of APIs. We provide following apis:

• push_front
• pop_front
• push_back
• pop_back
• delete
• iter - Returns a double ended iterator. Stops returning values when pointers meet. Immutable, the list remains intact.
• inter_into - Returns a double ended iterator that consumes the elements. List becomes empty, oncethe iterator is fully traversed.

Let's look at the Node and List definitions next.