Support NumPy ufuncs that require more than one argument

[apdavison]

i.e. "power", "fmod", "arctan2, hypot, ldexp, maximum, minimum"

Example of current problem:

In [1]: from lazyarray import larray, power

In [2]: x = larray([1, 4, 9, 16])

In [3]: power(x, 0.5)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-b294233f7ade> in <module>
----> 1 power(x, 0.5)

TypeError: larray_compatible_ufunc() takes 1 positional argument but 2 were given

[apdavison]

cf NeuralEnsemble/PyNN#358