Physics only mode that wouldn't require the HTML5 canvas

[quinton-ashley]

This would be useful for creating authoritative multiplayer servers with p5play.

This feature will be implemented via a flag like p5play.physicsOnly = true. It will prevent p5.js canvas rendering functions from being called.

For now, the npm canvas package would need to be used: https://www.npmjs.com/package/canvas

[quinton-ashley]

This can now be done by using noCanvas() in setup, disabling sprite drawing allSprites.autoDraw = false, and not attempting to draw anything else to the canvas.