Added new server/cmdline/io programmers' guide.

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

 ---
-layout: default
+layout: tutorial
 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: streams/
 next-title: "Use Streams for Data"
 prev: polymer-intro/
 prev-title: "Define a Custom Element"
 rel:
@@ skipping 259 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 %}