Implemented a double-ended queue (or deque) with the following API:
public class Deque<Item> implements Iterable<Item> {
public Deque() // construct an empty deque
public boolean isEmpty() // is the deque empty?
public int size() // return the number of items on the deque
public void addFirst(Item item) // insert the item at the front
public void addLast(Item item) // insert the item at the end
public Item removeFirst() // delete and return the item at the front
public Item removeLast() // delete and return the item at the end
public Iterator<Item> iterator() // return an iterator over items in order from front to end
}