drdavis/pygram11: 0.4.0

A breaking change to the API w.r.t. returns. All functions now return sum of weights squared, even if it's None. The histogramming functions previously had a single array returned if weights were not used. Now None is returned if no weights are used

>>> x = np.random.randn(1000)
>>> w = np.random.uniform(0.5, 0.8, x.shape[0])
>>> pygram11.histogram(x, bins=5, range=(-3, 3)
(array([ 30., 249., 450., 227.,  41.]), None)
>>> pygram11.histogram(x, bins=5, range=(-3, 3), weights=w)
(array([ 19.97159325, 162.31069262, 291.30576246, 147.4478516 ,
        27.12625336]), array([ 3.66815712, 10.36897935, 13.85860416,  9.86909866,  4.27544407]))