Make d a presentation attribute on path

[nikosandronikos]

Resolved that for now d will become a presentation attribute (no name change) with path data string as a value and for now it only affects the path element.

https://www.w3.org/2016/04/21-svg-minutes.html#resolution03

Need to update https://svgwg.org/svg2-draft/paths.html#DProperty

[Tavmjong]

Removed need for path() in 'd' value. Commit 0753aed5f7932f03123d3d94fb2533d402ea4455
Should complete making 'd' a property.