This example demonstrates basic geometry rendering, using the 
"vertex-at-a-time", or immediate rendering mode.  It also shows how geomety
can be represented by a set of points, lines, or triangles, with the latter-
most providing the most realistic, solid appearance.

The key commands are:

i, k - translate in x
j, l - translate in y
u, o - rotate around z axis
p, ; - uniformly scale
Space - reset transforms
d - change draw mode (cycles through triangles, points, and lines)
