add in SVG parsing

[Pomax]

The old SVG parsing was throwaway code and was never part of the public API. I've ripped it out so so it can be done properly. An implementation task list:

• [ ] PolyBezier.fromSVG(path) for accepting a full path
  • [ ] convert any line (LVH) into a quadratic {S, (S+E)/2, E}
  • [ ] convert any elliptical arc (A) into one or more cubics
• [ ] Bezier.fromSVG(pathsegment) for accepting individual curves (note that arcs cannot be supported by this call)
• [ ] PolyBezier.toSVG(), as aggregate call for all contained Bezier objects
  • [ ] remember to replace a b M a b with just a b (because each Bezier toSVG() starts with M)
• [x] Bezier.toSVG(), already implemented

To make this easier, path normalization can be taken from https://github.com/Pomax/svg-path-reverse/blob/gh-pages/reverse.js

[nathanwinder]

https://github.com/thednp/svg-path-commander has implemented a lot of this.

[Pomax]

But does way more than is needed here, and at almost 10x the size of this library, definitely not happening.