add benchmark and cell doc

benchmarks/fib.ce

@@ -0,0 +1,16 @@
+var time = use('time')
+
+function fib(n) {
+  if (n<2) return n
+  return fib(n-1) + fib(n-2)
+}
+
+var now = time.number()
+var arr = [1,2,3,4,5]
+for (var i in arr) {
+  log.console(fib(28))
+}
+
+log.console(`elapsed: ${time.number()-now}`)
+
+$_.stop()