Implement multiplication by naive algorithm
Implement multiplication by naive algorithm

This commit completes the implementation of the O(n^2) implementation
of 2-integer muliplication. Digits are carried when necessary and the
final 'addition' step of the algorithm is done by keeping a running
sum of each indiviual product multiplied by an appropriate 'tens'
multiplier.

timpel/stanford-algs,timpel/stanford-algs