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

@iwehrman has been reading all the config properties in the constructor, and then setting specific properties on the renderer. The long term goal of this is to have better documentation via JSDocs.

So, when in Rome, let's do this in the constructor for the SVG renderer (not the base renderer, where all the other configs are):

```javascript
if (config.hasOwnProperty("svgomg-enabled")) {
  this._useSVGOMG = !!config["svgomg-enabled"];
}
```

And, then add the property to the prototype with JSDoc like:

```javascript
/**
 * @type {boolean=}
 * [some description here]
 */
SVGRenderer.prototype._useSVGOMG = undefined;
```

Then, we don't need to hold on to the `config` object in `this`, and we'll need to update the conditional in `_getData`