Class WithinAbsMatcher

tests/catch.hpp:3026–3033

        enum class FloatingPointKind : uint8_t;

        struct WithinAbsMatcher : MatcherBase<double> {
            WithinAbsMatcher(double target, double margin);
            bool match(double const& matchee) const override;
            std::string describe() const override;
        private:
            double m_target;
            double m_margin;
        };

        struct WithinUlpsMatcher : MatcherBase<double> {
            WithinUlpsMatcher(double target, int ulps, FloatingPointKind baseType);