[plt-scheme] Re: opengl binding

sgl maps names like glSomeFunction to a more schemely some-function.
But there's glBegin... Easiest thing is to import with a prefix,
e.g. (require (prefix gl: (lib "sgl.ss" "sgl"))).  Note that sgl.ss
defines a more schemely interface generally (symbols for numeric
constants and so on); there's also gl.ss which gives a more literal
mapping. 

It is possible to use sgl from mzscheme 2xx, though you'll need to
build a bespoke version, and have some way to get a GL context (I used
GLUT, which I'd not recommend).

John