Check current args entry against a "bool" opt (ie. --[no-]progress).
If opt matches positively, out will be set to 1, or if opt matches
negatively, out will be set to 0, and in both cases 1 will be returned.
If neither the positive or the negative form of opt matched, out will be -1,
and 0 will be returned.
Check current args entry against a "bool" opt (ie. --[no-]progress). If opt matches positively, out will be set to 1, or if opt matches negatively, out will be set to 0, and in both cases 1 will be returned. If neither the positive or the negative form of opt matched, out will be -1, and 0 will be returned.