Add Two Linked List-ish Numbers

Given two integers represented as linked-lists, find their sum and return it in the form of linked list.

Note: You can assume that the input integers are non negative and the digits stored in the linked lists are in the reverse order. Take a look at the examples to understand the format.

Example:

Input 1: 1->2->3
Input 2: 1->2->3  
Output : 2->4->6 

Input 1: 9->9
Input 2: 9->8 
Output : 8->8->1