Proposal & WIP: add support for PDF output using tdewolff/canvas

[tdewolff]

I've been working on some boilerplate to make the Renderer interface work on my https://github.com/tdewolff/canvas library. See https://github.com/tdewolff/canvas/blob/master/gochart.go for the implementation and see https://github.com/tdewolff/canvas/tree/master/examples/go-chart for an example of the stock exchange example. Font support is still lacking since go-chart uses truetype.Font while canvas requires the whole font for embedding.

canvas has SVG, raster images (PNG, GIF, JPG...), PDF and EPS (in progress), WASM Canvcas (https://tdewolff.github.io/canvas/examples/html-canvas/) output formats, and I'm planning OpenGL / WebGL support too. Let me know what you think and whether we could integrate both libraries if you're interested?

Example output:

PS: I wanted to contact you privately but I couldn't find an e-mail address of yours nor am I able to send a message through LinkedIn...but perhaps you prefer to keep it hidden, I can understand that!