Time for action – summoning up the zombies

1. Add a new class called Enemy to the Gemstone Hunter project.

2. Add the following using directives to the Enemy class:

   using Microsoft.Xna.Framework;
   using Microsoft.Xna.Framework.Content;
   using Microsoft.Xna.Framework.Graphics;
   using Tile_Engine;

3. Modify the class declaration for the Enemy class to make it public and derive it from the GameObject class:

   public class Enemy : GameObject

4. Add declarations for the Enemy class:

   private Vector2 fallSpeed = new Vector2(0, 20);
   private float walkSpeed = 60.0f;
   private bool facingLeft = true;
   public bool Dead = false;

5. Add a constructor for the Enemy class:

   #region Constructor
   public Enemy(ContentManager content, int cellX, int cellY)
   {
       animations.Add("idle",
           new AnimationStrip(
               content.Load<Texture2D>(
                   @"Textures\Sprites\MonsterC\Idle"),
               48, 
               "idle"));
       animations["idle"].LoopAnimation = true;
   
       animations.Add("run",
           new AnimationStrip...