title: libGDX: How to let the camera point to moving sprite?
body: <p>I'm new to libGDX and android game dev. And I want to achieve this: 
  I have a <code>Screen</code> and within it, a ball sprite that is moving along the X axis. Now I want to center the viewport to the sprite when it moves. Just like in Angry birds, where the camera follows the bird flying across the sky.</p>
  
  <p>How can I implement that within my game using <code>OrthographicCamera</code>?</p>