Implement `beginContour()` and `endContour()`

[matthew-carroll]

Implement beginContour() and endContour()

These run within a beginShape() and endShape(). The contour represents a hole cut out of the overall shape.

[ThangVuNguyenViet]

Hi @matthew-carroll, can you assign me this one? Although this is quite difficult, as I read the java implementation, I did get some insight into doing this.

[matthew-carroll]

Sure. This ticket will have a much higher bar than the previous one, but you're welcome to give it a try. I'm not even sure if this ticket is reasonably possible without Canvas supporting the necessary splines, but if you think you can make it work, then go for it.

[ThangVuNguyenViet]

Sure. I'll try my best

[ThangVuNguyenViet]

I removed my assignment. The bar is too high for me to to this