implementing native functions (ch24)

samples/ch24_fib.lox

@@ -0,0 +1,9 @@
+fun fib(n) {
+    if (n < 2) return n;
+    return fib(n - 2) + fib(n - 1);
+}
+
+var start = clock();
+
+print fib(20);
+print clock() - start;