Method SummaryColumn

unittests/catch.hpp:12081–12083

struct SummaryColumn {

    SummaryColumn( std::string _label, Colour::Code _colour )
    :   label( std::move( _label ) ),
        colour( _colour ) {}
    SummaryColumn addRow( std::size_t count ) {
        ReusableStringStream rss;
        rss << count;