Enabled v-sync in OpenGL and Pong examples (to make them smoother)

examples/pong/Pong.cpp

@@ -28,6 +28,7 @@ int main()
 
     // Create the window of the application
     sf::RenderWindow window(sf::VideoMode(gameWidth, gameHeight, 32), "SFML Pong");
+    window.EnableVerticalSync(true);
 
     // Load the sounds used in the game
     sf::SoundBuffer ballSoundBuffer;