Enable mismatching dimensions in broadcast_arrays

[njlivesey]

It's great to have broadcast_arrays working, but I'm not sure we need to require matching dimensionality. (Sorry if I should have moved this from a discussion to an issue sooner.)

Consider

import numpy as np
import pint

ureg = pint.UnitRegistry()

T = np.ones(shape=[10,1]) * 250.0 * ureg.K
v = np.ones(shape=[1,10]) * 10.0 * ureg.m / ureg.s
rho = np.ones(shape=[10,10]) * ureg.kg / ureg.m**3       
        
T, v, rho = np.broadcast_arrays(T, v, rho)

Many thanks