added hello peasy offscreen example

[cansik]

I have added an example with a P3D offscreen canvas, which is drawn onto a P2D context. To use peasycam in this scenario, you have to apply the state of the current cam to the canvas.

// apply view matrix of peasy to canvas
cam.getState().apply(canvas);

I have used another rendering (cube with a sphere) as the hellopeasy example, but if you would like to have consistency over all examples, I could change that.

[jdf]

Thank you.