add numerical recipes library

lib/nr/k_and_r/recipes/metrop.c

@@ -0,0 +1,11 @@
+
+#include <math.h>
+
+int metrop(de,t)
+float de,t;
+{
+	float ran3();
+	static long gljdum=1;
+
+	return de < 0.0 || ran3(&gljdum) < exp(-de/t);
+}