ENH: Function to find the largest element and its index

[seberg]

Sometimes it is convenient to find the largest element and it's index at the same time. Of course finding the largest element can already be achieved with max().

The largest_element() function should return a tuple of value, index.

Working on this issue

This function already exists as a stub with some documentation. We have already provided a basic test as well.

• Find and expand the largest_element stub with an implementation.
• Find the test_largest_element test, and remove the @pytest.mark.xfail. Hopefully, the test passes now!
• Commit your changes and create a PR.