add membench-NX - open source memory benchmark tool

also remove memtester, it doesnt really work

Source/Membench-NX/source/gpu_bw.h

@@ -0,0 +1,4 @@
+#pragma once
+#include <stdbool.h>
+
+bool gpu_bw_run(bool is_4gb, double *copy_out, double *read_out, double *write_out);