title: Animate drawing of CALayer with spring animation
body: <p>I want to animate <a href="https://stackoverflow.com/questions/7991086/iphone-core-animation-drawing-a-circle">drawing an arc onscreen</a> but I want it to have the spring effect found in iOS 7's <code>UIView animate... usingSpringDamping:</code> API. I know I can use Core Animation directly by creating a <code>CABasicAnimation</code> but then I lose out on the nice spring effect, and the built-in timing functions stop at <code>EaseOut</code>, which isn't really what I want. Ideally the arc would draw to a target angle, overshoot it, then bounce back and forth until it settled on the target.</p>
  
  <p>Is there a way to do this without writing my own timing function / subclassing <code>CAAnimation</code>?</p>