experimental SVG support

Adds a feature flag "svgomg-enabled" that directs SVG exports at an experimental SVG export engine: https://github.com/adobe-research/svgObjectModelGenerator

I'm a bit concerned about having this point to master rather than a SHA or other "release" branch/tag.

By having it point to master, you don't really know what you're going to get when T-bone happens to decide to integrate to perforce.

My first choice would be to point to a SHA. Would this make your workflow really difficult? If that doesn't make sense, then making a "release" branch and integrating from master to release would probably be the next best thing.