assignment1 KNN classifier L2 distance

[aishik-pyne]

The functions
compute_distances_two_loops
compute_distances_one_loops
compute_distances_no_loops
all are required to compute the L2 distance so the dists matrix should be prepended by np.sqrt in all the cases

[haofengsiji]

Sometimes , it is more covenient to work with mathematically and computationally by using squared L2 norm instead of L2 norm. It's true.