Method pluralise

tests/catch.hpp:11157–11160

    }

    pluralise::pluralise( std::size_t count, std::string const& label )
    :   m_count( count ),
        m_label( label )
    {}

    std::ostream& operator << ( std::ostream& os, pluralise const& pluraliser ) {
        os << pluraliser.m_count << ' ' << pluraliser.m_label;