RaggedArray fails with len(shape) >= 3 and slices

[justinrporter]

a = ra.RaggedArray([[[0, 1, 0, 1],
                     [0, 1, 0, 1]],
                    [[1, 1, 1, 1, 0],
                     [0, 0, 0, 0, 1]]])

a[:, :, 0]

Fails with

ValueError                                Traceback (most recent call last)
<ipython-input-5-caa57490a0a5> in <module>()
----> 1 a[:, :, 0]

/Users/jrporter/projects/enspara/enspara/util/array.py in __getitem__(self, iis)
    458         # tuples get index conversion from 2d to 1d
    459         elif type(iis) is tuple:
--> 460             first_dimension, second_dimension = iis
    461             # if the first dimension is a slice, converts both sets of indices
    462             if type(first_dimension) is slice:

ValueError: too many values to unpack (expected 2)

So does a[:, 0, :] and a[0, :, :].

Also, the dtype of a is object, which isn't what I expected (since they're ints) and the shape is [2, 2, None] where I expected [2, None, 2]...

[mizimmer90]

see #164