Commented out the printing of data in SpriteBatch and let RenderSystem finish its preUpdate() after it calls stopGame so it will call spriteBatch.begin() and not cause errors later
Added a bunch of entities. Forgot to mention that the last commit made all entities move to the right a bit every frame in RenderSystem
Added some time measurement to see how much time each system is taken and also how much time it takes for the whole frame. Currently it's just printed to the console. Also the last 2 are always way off
Updated README with note about a library being used by different parts of the engine