add numerical recipes library

lib/nr/cpp/recipes/metrop.cpp

@@ -0,0 +1,10 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+bool NR::metrop(const DP de, const DP t)
+{
+	static int gljdum=1;
+
+	return de < 0.0 || ran3(gljdum) < exp(-de/t);
+}