Hook to node rendering

[JordanValdma]

A hook callback function that can modify the canvas circle (node element). I have implemented changing circle to a pie, but not sure how to merge it decently to the framework.

[jacomyal]

In the new version, it is possible to add your own custom node renderer. You will find some more documentation here.

Also, here are some precisions:

• If you want to customize node rendering, do not forget that you have to do it for each renderer (Canvas, WebGL, and more when more renderers will be implemented).
• Every node renderers will not be systematically merged, since different people will always need different renderers.