refactored ClusterFinder and find_clusters, add clusterfinder_benchmark, refactored main in benchmarks

benchmarks/ndarray_benchmark.cpp

@@ -128,6 +128,4 @@ BENCHMARK_F(TwoArrays, MultiplyAddDivideWithIndex)(benchmark::State &st) {
         }
         benchmark::DoNotOptimize(res);
     }
-}
-
-BENCHMARK_MAIN();
+}