Don't bail on passwords longer than 72 chars

[Goorzhel]

For reference, zxcvbn's signature.

Why not zxcvbn(max_length=ARBITRARILY_HIGH_NUMBER)?

I reasoned that max_length exists to prevent arbitrarily-long strings from sucking up too much CPU time.

>>> from zxcvbn import zxcvbn
>>> from timeit import timeit
>>> test = lambda i: zxcvbn(password="a"*i, max_length=i)
>>> timeit(lambda: test(100), number=1)
0.02540450499873259
>>> timeit(lambda: test(500), number=1)
2.764077340001677

(Of course, a string like "a"*500 will still score 1, but that's an edge case this PR shan't deal with.)