TODO
====
- package vignette 
- win32: window icon
- rgl.bbox labels
- z-sorted alpha-blended surfaces
- R namespaces
- pixmap index format
- z-distance sorted rendering of alpha-blended faces 
- bbox: non-uniform scale per axis
- embedded multi-threaded framework
- 3d util functions
- parametric shapes
- spheres,bg: specify sections and segments 
- bg: sphere horizontal color range
- multi-pass rendering (through accumulation) ... depth of field?!
- win32/visualc++: built resets fpu word (detected with options(warn.FPU=t) )

