Simple interface for using GLPK in Python.

This requires GLPK to be installed, and uses the SWIG package for
producing the API.

Please see the end of 'glpk.py' or 'example.py' for simple usage
examples.

The file 'example_refman.py' reproduces in python the example provided
(in C) in glpk's reference manual.

Notice that the glpk's C keyword 'in' is renamed '_in' in Python, for
avoiding conflict.
