Added Hamming Distance (#340)
Added Hamming Distance (#340)

In learning.py, I added the Hamming Distance metric.
sofmonk/aima-python,SnShine/aima-python,sofmonk/aima-python,Chipe1/aima-python,aimacode/aima-python,Chipe1/aima-python,jo-tez/aima-python,jo-tez/aima-python,SnShine/aima-python,aimacode/aima-python