Write to svg

@simpsus Take a look! This writes out SVG files, and uses no external libs. I think the code is pretty clean, too.

I used [this O'Reilly guide](http://commons.oreilly.com/wiki/index.php/SVG_Essentials) for learning about the SVG format.

There are still some TODOs, but it's pretty far along:
- [ ] use `#ff3300` color format instead of `rgb(255, 60, 0)`, for smaller SVG files
- [ ] use Bezier curves, for smaller SVG files, and smoother curves. (I have a Processing sketch that should help w/ the `PathIterator` parts of this. It's easy to do, but hard to figure out.)

I was thinking of adding some metadata to the SVG. Is this crazy? Do people use this? I don't often use SVGs, so I can't tell. Something like:
```xml
<svg>
  <title>${sketch.getTitle()}</title>
  <desc>Made with processing.org and wordcram.org.</desc>
  <g id="${word.id}" word="${word.word}">
    ...
  </g>
</svg>
```