track the canvas context's transform

[kevinbarabash]

This is useful for processing-js as well as other canvas based libraries.

https://www.safaribooksonline.com/blog/2012/04/26/html5-canvas-games-tracking-transformation-matrices/

[kevinbarabash]

There's even a handy node module for this: https://github.com/MellowMelon/canvas-transform