Added row and column class refernences to Array2D
This PR introduces two new private class variables for the Array2D
_rowclass_columnclass
which are used by Array2D.__getitem__ to decide how to return items from the 2-d array.
This PR introduces two new private class variables for the Array2D
_rowclass_columnclasswhich are used by Array2D.__getitem__ to decide how to return items from the 2-d array.