Method usage

tests/catch.h:4469–4478

        }

        void usage( std::ostream& os, std::string const& procName ) const {
            validate();
            os << "usage:\n  " << procName << " ";
            argSynopsis( os );
            if( !m_options.empty() ) {
                os << " [options]\n\nwhere options are: \n";
                optUsage( os, 2 );
            }
            os << "\n";
        }
        std::string usage( std::string const& procName ) const {
            std::ostringstream oss;
            usage( oss, procName );