unix: Add an attribut 'options_behaviour' to 'Host' class allowing to define if
options must be put before or after arguments (default: before) when executing a
command. There's also a context manager for this behviour.
unix: Add a context manager for connecting to a remote a host.
unix: Add a class for managing users.
unix: Add a class for managing groups.
unix: Add a class for managing processes.
unix: Add methods for mount/umount commands.
unix: force conversion of all command arguments to string.
unix: Use pythonic version of execute for uname fonctions.
unix: Some coding style changes.
unix: Use six.iteritems() for python 2/3 compatibility.
unix: Add some strings compatibilty between python 2/3.