BTW I decided to add these properties directly to the `Table` class as they can be useful and make the table feel a little more numpy/scipy.sparse-ish.

Another note, we were previously referring to the number of non-zero entries as `size` throughout the codebase, but I changed this to `nnz` to match scipy.sparse. `size` was also confusing to me because an ndarray's `size` attribute is the total number of elements (e.g., rows x cols).