multi-dim pdarrays to print like numpy

[ajpotts]

This example shows they are different:

In [65]: ak.array(npa)
Out[65]: array([array([4 3 7 2 9]) array([6 3 1 9 2]) array([6 6 8 9 6]) array([5 7 3 7 5]) array([1 5 4 2 7])])

In [66]: npa
Out[66]: 
array([[4, 6, 6, 5, 1],
       [3, 3, 6, 7, 5],
       [7, 1, 8, 3, 4],
       [2, 9, 9, 7, 2],
       [9, 2, 6, 5, 7]])