add svg.PathData. It will decouple the path DSL from the <path> builder.
change svg.Path to use svg.PathData. Update tests.
add several enums for dealing with animation.
add svg.ClockValue for representing time in animations.
add svg.Key and svg.ContinuedKey for managing key splines in animations.
add svg.AnimationElement, to be a base class for animation builders.
add svg.animate for building <animate> elements. Add tests too.
add svg.animateMotion for building <animateMotion> elements. Add tests too.
add svg.mpath for building <mpath> elements. Add tests too.
add builders for <animateColor>, <animateTransform>, and <set>. No tests so far.