Add libconfig implementation and tests

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add a generate_optstring() function to libcommon

This function generates the optstring argument exepected by getopt_long
from a NULL-terminated struct option array.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Load session daemon options from configuration file

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Load relay daemon options from configuration file

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>