fix tools._scalar_out to account for Series.item deprecation

[wholmgren]

tools._scalar_out calls input.item() to reduce an array or Series to a scalar. But the Series.item method is deprecated as of pandas 0.25, so we need to do something different. Maybe first call np.asarray so we know we have a numpy array and then we can call .item().

Also should replace the reserved argument name input with something else.