This code example shows how to build the OpenGL orthographic projection matrix.  You can
toggle between the orthographic and frustum calls and see the difference between them, 
using the same frustum parameters.

Controls
--------
ESC: quit
w, s: move near plane out and in
e, d: move far plane out and in
i, k: move view window up and down
j, l: move view window left and right
p: toggle between orthographic and perspective projection
SPACE: reset to start
