Add svg properties.

[watanabeyu]

I'm using SVG animation and I'd like support for types corresponding to SVG-specific properties like y.

[askoufis]

y (and other geometric properties) is only supported in CSS in browser that implement the SVG 2.0 spec, which I don't think any browser fully support yet. I think Chrome implements some of it, but until there's broader support, both in browsers and the csstype package, this probably won't be implemented anytime soon.