Moved GLU.jl into OpenGL.jl and added some more tuts/features to SDL/GLUT packages

- Followed the lead of some other OpenGL implementations (e.g., http://pyopengl.sourceforge.net/) and moved GLU.jl files into the OpenGL.jl package.  SDL/GLUT examples have been appropriately updated.

- Added some more NeHe tuts, as well as an example of using a joystick (untested since I don't have access to a joystick at the moment).  This will be the last set of NeHe tuts that I do, since I'm getting a bit bored of them and they only cover OpenGL 1.x functions (i.e., they are pretty old).

- Made SDL keyboard processing examples much "smoother" for the user.

--Rob