Generate doxygen doc for pyfaust.constraints, pyfaust.params and pyfaust.demo...

Generate doxygen doc for pyfaust.constraints, pyfaust.params and pyfaust.demo and add a script to avoid fake namespaces generation.

- The script ./gen_doc/py_filterout_namespace.py filter out the @namespace tag lines generated by doxypypy when they doesn't match a real py. module (e.g. an attribute).
- py_filter scripts (doxypypy bash/batch launchers) call py_filterout_namespace.py to filter bad namespaces generated when using doxypypy --ns option (needed to have submodules correctly positioned into pyfaust by doxygen).