Paraboloid OpenSCAD Script

Ever wanted a elliptic paraboloid solid for OpenScad? Here it is!

What is a parabolic reflector good for?
Solar cookers, parabolic microphones, satellite dishes, spotlights reflector
http://en.wikipedia.org/wiki/Parabolic_reflector

Parabolic reflectors focus parallel rays at a focus point (e.g. sun rays).
And it can make circular rays at the focus point go parallel in one direction (spotlight).

It seems to be "similar" to the nose cone design of aircraft and model rockets, too. http://en.wikipedia.org/wiki/Nose_cone_design

Usage :
paraboloid (y=50,f=10,rfa=0,fc=0,detail=44);

To create a paraboloid choose following parameters:
- height (y); This defines the vertical height
- focus length (f); This defines the distance of the focus point from the top
- radius of focus area (rfa); You can have a focus circle (rfa>0) instead of a focus point (rfa=0)
- center focus center (fc); Choose the center on top (fc=0) or center in focus point (fc=1)
- fine struct