* PARSE_OPT_OPTARG: says that the argument is optionnal (not for BOOLEANs)
* PARSE_OPT_NOARG: says that this option takes no argument, for CALLBACKs
* PARSE_OPT_NONEG: says that this option cannot be negated
* PARSE_OPT_OPTARG: says that the argument is optionnal (not for BOOLEANs)
* PARSE_OPT_NOARG: says that this option takes no argument, for CALLBACKs
* PARSE_OPT_NONEG: says that this option cannot be negated