adding new command-line app tutorial

src/site/docs/tutorials/futures/index.markdown

 ---
 layout: default
 title: "Use Future-Based APIs"
 description: "A first look at Futures and how to use them to make your asynchronous code better."
 has-permalinks: true
 tutorial:
   id: futures
-next: fetchdata/
-next-title: "Fetch Data Dynamically"
+next: cmdline/
+next-title: "Write Command-Line Apps"
 prev: polymer-intro/
 prev-title: "Define a Custom Element"
 rel:
     author: shailen-tuli
 ---
 
 {% capture whats_the_point %}
 
 * Dart is single-threaded.
 * Synchronous code can make your program freeze.
@@ skipping 252 matching lines @@
 uses a Future when doing an HTTP request.
 
 * The example featured in
 [Use IndexedDB](/docs/tutorials/indexeddb/)
 uses many Futures when interacting with the database.
 
 {% endcapture %}
 
 {% include tutorial.html %}