Into the vortex she whirled and spun and finally
rotated to a halt!

Concept 1.5 : Rotate
==================

Idea:
=====
glRotatef(angle, x, y, z) allows one to rotate
an object about any axes, before rendering the object.  
In the above function, the angle specifes the angle
by which to rotate, x, y, and z specify the axis of
rotation.  For example (30, 1.0, 0.0, 0.0) would
imply ' rotate 30 degrees about the X-axis'.  The
object is rotated by angle (in degrees) in a counter
clockwise direction (CCW) about the ray from the 
origin to (x, y, z) i.e. if the rotation is viewed 
from (x, y, z) looking towards the origin it appears CCW

Experiment
==========
Try different values for angle and x, y, z 
Can you tell the color of the back of the cube?
If yes, how about the color of the bottom face?

Note:
=====
One can perform multiple rotations on an object just
like we saw in the case of translations.
Also we can use glPushMatrix() and glPopMatrix() to 
perform rotations on two different objects as we did
in the case of translations.