Additional Indexing functionality in `ArrayView`

[stress-tess]

Update ak.ArrayView indexing to be able to do everything shown in the numpy basic indexing tutorial. We currently only handle integer array indexing and a mix of ints and slices

Namely we need to:

• [ ] Make changing x.shape equivalent to a x.reshape operation

>>> x = np.arange(10)
>>> x.shape = (2, 5)
>>> x[1, 3]
8

• [ ] Add support for Dimensional indexing tools
  • Ellipsis expands to the number of : objects needed for the selection tuple to index all dimensions
  • newaxis: Each newaxis object in the selection tuple serves to expand the dimensions of the resulting selection by one unit-length dimension
• [ ] Assigning slices of an ArrayView to another pdarray/ArrayView
• [ ] Advanced indexing
  • This gets especially hairy when mixing basic and advanced indexing...

Advanced indexing is triggered when the selection object, obj, is a non-tuple sequence object, an ndarray (of data type integer or bool), or a tuple with at least one sequence object or ndarray (of data type integer or bool). There are two types of advanced indexing: integer and Boolean.