Day 17 Recap Questions
  1. How do you implement add_front on a linked list?
  2. How do you modify a singly linked list to create a doubly linked list?
  3. How do you make a copy of a singly linked list?
  4. Why does add_after takes a Node * as input, but add_front takes Node **?
  5. What cases should be handled when implementing remove_front?