Function mean

lib/catch2/catch.hpp:6991–6995

            template <typename Iterator>
            double mean(Iterator first, Iterator last) {
                auto count = last - first;
                double sum = std::accumulate(first, last, 0.);
                return sum / count;
            }

            template <typename URng, typename Iterator, typename Estimator>
            sample resample(URng& rng, int resamples, Iterator first, Iterator last, Estimator& estimator) {