ofxSVG improvements

Hi everyone!

I’ve been working on some improvements to ofxSVG, primarily to improve compatibility with certain SVGs.

Nerdy details - I’ve implemented the “use” element by editing the SVG string before it is parsed. There’s a minor performance hit, but only if the SVG needs fixing. (The underlying Libtinysvg library doesn’t support this tag). Maybe we could implement some of the other missing elements? Like ellipse?

If you regularly use SVGs, I’d love to know what you think and it’d be great if you could test it with your SVG files. It’s now been integrated into the master branch, the commit is here.