[Numpy-discussion] #4808 -- let np.pad default to constant

[Stefan van der Walt]

In PR 4808, I propose changing the default padding mode (for `np.pad`)
to constant (0).

It was suggested that I mention the change here, in case someone has a
use case or argument for not making it.

https://github.com/numpy/numpy/pull/4808

Thanks!
Stéfan