Remove from pyglet.gl import *

[MatthieuBizien]

Remove from pyglet.gl import *, and replace it with from pyglet import gl, as it's not recommended in the PEP8.

Wildcard imports (from import *) should be avoided, as they make it unclear which names are present in the namespace, confusing both readers and many automated tools.

Like #35, I believe that project is a great educational tool, an impressive achievement, and a reference for clean Python code.