remove some of the bloat, how can we make things more compact?

i.e. if not using 3D, can leave out PGraphics3, PTriangle, PLine

PPolygon isn't currently used for anything, should remove it, or break it
into its own version of PGraphics3 that can be used at one's own risk.

this is too general a goal, so closing it out.

the better solution is to implement a simple proguard optimization step
after sketches have been created, that will make them more reasonable, and
strip unused code. (will open a separate bug for that.)