Animate path attribute 'd'

We now attribute the 'd' attribute of SVG path elements.

This is used by the LA Times spinner, which we do not yet render
correctly - we do not interpolate arcs or bezier curves correctly.
Interpolate path parameters

Animation of SVG's path attribute, 'd', is achieved by interpolating the
individual parameters of each path segment.

http://www.w3.org/TR/SVG/paths.html#DAttribute
Merge pull request #53 from ewilligers/path-interpolate-parameters

Path interpolate parameters