2020-07-23
	Changed libconfig to be optionnal. Source needs to
	be compiled with -DCONFIG and linked with -lconfig
	if support is wanted. `conffile_option` is ignored
	(and will be considered illegal command line) if
	libconfig is disabled.

2020-07-19
	Changed *_cl_parse() API: now always returns, 0 on success and
	negative on error (before, it would exit() directly, which
	prevents the caller from picking a different parsing strategy,
	or choosing its exit codes)
