SVGAnimationElement methods and attribute

Animation elements such as set, animateTransform etc, have
- targetElement
- getStartTime()
- getCurrentTime()
- getSimpleDuration()

We test these methods on an animateMotion element.

These are specified in
http://www.w3.org/TR/SVG/animate.html#InterfaceSVGAnimationElement
Merge pull request #28 from ewilligers/get-simple-duration

SVGAnimationElement methods and attribute