Research pure JS rendering

[Mr0grog]

Look into whether we could render in pure JS as well as through node-canvas. It's possible we could be speedier by not crossing the JS/C++ boundary. This would probably let us do some crazier things like different blending modes, too.

That said, however, this will be a lot of work for (likely) minor gain. We have bigger optimization bottlenecks at the moment.

[bensheldon]

A start at least for how to render a png: npmjs Not sure if we want to define an intermediary format (e.g. SVG) and worry about the actual rasterization later.