title: Prevent shapes from clipping into each other
body: <p>I just started to port my game to slick2d and I want mine entities to collide with each other.<br>
  I know that <code>shapeA.intersects(shapeB)</code> checks if two shapes intersect but I want them to collide so that they aren't able to overlap each other.<br>
  I would be easy if the shapes were only rectangles but that's not the case.<br>
  So is there any way to perform this in an efficent way?</p>