Update Breakout progress code for PowerUps chapter. Also few missed items on prev. progress code.

src/7.in_practice/3.2d_game/0.full_source/progress/5.game.h

@@ -12,6 +12,8 @@
 #include <glad/glad.h>
 #include <GLFW/glfw3.h>
 
+#include "game_level.h"
+
 // Represents the current state of the game
 enum GameState {
     GAME_ACTIVE,
@@ -49,6 +51,8 @@ public:
     bool                    Keys[1024];
     bool                    KeysProcessed[1024];
     unsigned int            Width, Height;
+    std::vector<GameLevel>  Levels;
+    unsigned int            Level;
     // constructor/destructor
     Game(unsigned int width, unsigned int height);
     ~Game();