Sum Lists

You have two numbers represented as lists, where each element contains a single digit. The digits are stored in reverse order (1's digit first).

Write a function that adds the two numbers and returns the sum as a list (also in reverse order).

Example:

Input:  [7, 1, 6] + [5, 9, 2]   →  617 + 295
Output: [2, 1, 9]               →  912