title: SpriteKit SKAction easing
body: <p>Well the title gives the question away, how can I apply easing to the SKAction node actions in SpriteKit?</p>
  
  <p>I found that this works:</p>
  
  <pre><code>SKAction *moveAction = [SKAction moveByX:moveX y:moveY duration:0.5];
  moveAction.timingMode = SKActionTimingEaseInEaseOut;
  [node runAction:moveAction];
  </code></pre>
  
  <p>However there are only a few easing types available <a href="https://developer.apple.com/library/ios/documentation/SpriteKit/Reference/SKAction_Ref/Reference/Reference.html">there</a>, namely Linear, EaseIn, EaseOut, EaseInOut. </p>
  
  <p>And those easing values are fixed and cannot be altered. I am looking for something like EleasticInOut. With preferably a bit more control. How can I create that?</p>