This demo shows the power of a simple scene graph, which allows for quick and
easy creation, management and rendering of hierachical scenes such as the
articulated tank used herein.  The demo allows the user to move and rotate
the tank, which turns the turret and barrel as well.  In addition, the turret
and barrel can be independently articulated, as well


The key commands are:

i, k - translate tank in x
j, l - translate tank in y
u, o - rotate tank around z
;, p - scale tank
a, d - rotate turret around z
w, s - rotate barrel vertically
space - reset all transforms
