Integrate Nonius benchmark into Catch2

Changes done to Nonius:
* Moved things into "Catch::Benchmark" namespace
* Benchmarks were integrated with `TEST_CASE`/`SECTION`/`GENERATE` macros
* Removed Nonius's parameters for benchmarks, Generators should be used instead
* Added relevant methods to the reporter interface (default-implemented, to avoid
breaking existing 3rd party reporters)
* Async processing is guarded with `_REENTRANT` macro for GCC/Clang, used by default
on MSVC
* Added a macro `CATCH_CONFIG_DISABLE_BENCHMARKING` that removes all traces of
benchmarking from Catch

include/internal/benchmark/catch_sample_analysis.hpp

@@ -0,0 +1,50 @@
+/*
+ *  Created by Joachim on 16/04/2019.
+ *  Adapted from donated nonius code.
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+// Benchmark results
+
+#ifndef TWOBLUECUBES_CATCH_BENCHMARK_RESULTS_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_BENCHMARK_RESULTS_HPP_INCLUDED
+
+#include "catch_clock.hpp"
+#include "catch_estimate.hpp"
+#include "catch_outlier_classification.hpp"
+
+#include <algorithm>
+#include <vector>
+#include <string>
+#include <iterator>
+
+namespace Catch {
+    namespace Benchmark {
+        template <typename Duration>
+        struct SampleAnalysis {
+            std::vector<Duration> samples;
+            Estimate<Duration> mean;
+            Estimate<Duration> standard_deviation;
+            OutlierClassification outliers;
+            double outlier_variance;
+
+            template <typename Duration2>
+            operator SampleAnalysis<Duration2>() const {
+                std::vector<Duration2> samples2;
+                samples2.reserve(samples.size());
+                std::transform(samples.begin(), samples.end(), std::back_inserter(samples2), [](Duration d) { return Duration2(d); });
+                return {
+                    std::move(samples2),
+                    mean,
+                    standard_deviation,
+                    outliers,
+                    outlier_variance,
+                };
+            }
+        };
+    } // namespace Benchmark
+} // namespace Catch
+
+#endif // TWOBLUECUBES_CATCH_BENCHMARK_RESULTS_HPP_INCLUDED