code: public static void popHeap(Quicksortable q, int size) {
          q.swap(0, size-1);
          heapifyDown(q, 0, size-1);
      }
docs: Pops the lowest element off the heap and stores it in the last element
  
  @param q The quicksortable to heapify down.
  @param size The size of the quicksortable.