IE compatibility! [Fixes #3]

Outstanding Issues:

* Performance?
  * Uses <core-animation> (web-animations.js) to overcome IE limitation of no SVG animations with CSS.
  * Either make Chrome/Firefox/Safari use <core-animation> and remove dead CSS, or only use <core-animation> for IE (causes redundant code)
* Either need to add the following to web-animations.js, or change to custom programatic animation effect and set attribute on SVG element directly:

```javascript
var propertyTypes = {
  //…
  strokeDashoffset: lengthType,
  strokeWidth: lengthType
};
```

* Unlike CSS animations, the easing function spans over the entire animation, not just between keyframes.