public static void AnimalShelter()
        {
            //enqueue, dequeueAny, dequeueDog, dequeueCat
            var shelter = new Shelter();

            shelter.Enqueue(new Animal("dog1", Species.Dog));
            shelter.Enqueue(new Animal("dog2", Species.Dog));
            shelter.Enqueue(new Animal("cat1", Species.Cat));
            shelter.Enqueue(new Animal("dog3", Species.Dog));
            shelter.Enqueue(new Animal("cat2", 0));

            Console.WriteLine(shelter.DequeueCat().ToString());
            Console.WriteLine(shelter.DequeueAny().ToString());
            Console.WriteLine(shelter.DequeueAny().ToString());
            Console.WriteLine(shelter.DequeueAny().ToString());
            Console.WriteLine(shelter.DequeueAny().ToString());
        }