v0.2.0

• Fix zooming if the mouse moves during a wheel gesture.
• Add zoom.translateExtent to constrain panning!
• Replace zoom.size with zoom.extent.
• The node argument to d3.zoomTransform is now required.
• Add d3.zoomIdentity.
• Change zoom.transform to not enforce the scale (or translate) extent.
• Change zoom.transform to define a “zoom” tween, not “zoom:zoom”.