Remove the readline completion hook fallback used with Python < 2.6

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Remove unused parameters in _complete_token_{command,path}()

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Use 2to3 in setup and mention that configshell-fb is Python 3 compatible

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>