add numerical recipes library

lib/nr/ansi/recipes/erffc.c

@@ -0,0 +1,8 @@
+
+float erffc(float x)
+{
+	float gammp(float a, float x);
+	float gammq(float a, float x);
+
+	return x < 0.0 ? 1.0+gammp(0.5,x*x) : gammq(0.5,x*x);
+}