add numerical recipes library

lib/nr/ansi/recipes/metrop.c

@@ -0,0 +1,10 @@
+
+#include <math.h>
+
+int metrop(float de, float t)
+{
+	float ran3(long *idum);
+	static long gljdum=1;
+
+	return de < 0.0 || ran3(&gljdum) < exp(-de/t);
+}