Added new benchmark script called countdown

Countdown is a microbenchmark that focuses on function calls.

Author: cesquivias

benchmark/countdown/countdown.mumbler

@@ -0,0 +1,20 @@
+(define countdown (lambda (n)
+                    (if (< n 101)
+                        (if (< n 1)
+                            0
+                            (countdown (- n 1)))
+                        (countdown
+                         ((lambda (x)
+                            (countdown 100)
+                            (- x 100))
+                          n)))))
+
+(countdown 10000)
+(countdown 10000)
+(countdown 10000)
+(countdown 10000)
+
+(define start (now))
+(countdown 10000)
+(define end (now))
+(println (list (quote computation-time) (- end start)))

benchmark/countdown/countdown.sl

@@ -0,0 +1,22 @@
+function countdown(n) {
+    if (n < 101) {
+        if (n > 0) {
+            countdown(n - 1);
+        }
+    } else {
+        countdown(100);
+        countdown(n - 100);
+    }
+}
+
+function main() {
+    countdown(10000);
+    countdown(10000);
+    countdown(10000);
+    countdown(10000);
+
+    start = nanoTime();
+    countdown(10000);
+    end = nanoTime();
+    println("computation time: " + (end - start) / 1000000);
+}