Support by tdewolff/canvas

[tdewolff]

Hi Will, I've added support for go-chart for the tdewolff/canvas library (see https://github.com/tdewolff/canvas). This allows rendering to a host of other targets, including PDF, EPS, SVG, OpenGL, HTMLCanvas, and Gio. Just wanted to let you know, posted it here as I was unable to find an e-mail address of you. If you're interested, we could merge efforts or mention each other in the readmes. Let me know!