Sorting & argsort

Implement functions that sort an array and, more usefully, find where each element would go. sorted_copy returns a sorted copy and leaves the input alone, sort_order returns the indices that would sort the array (a stable argsort), rank_of turns that order into each element's position, descending_order is the stable order from largest to smallest, and sort_rows_by_column reorders the rows of a 2D array by one column. Ties always keep their original relative order (a stable sort).