Enhancement proposal shadow mapping

[b2renger]

@cansik : It could be pretty neat to have some shadows available :
https://forum.processing.org/two/discussion/12775/simple-shadow-mapping

:)

[cansik]

Yes that sounds very interesting. The problem is that the current library is only using the 2d color information of the pixels, not the z-buffer. I have to check how we could implement this.