adding new command-line app tutorial

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

 ---
 layout: default
 title: "Fetch Data Dynamically"
 description: "Use HttpRequest to fetch data from a file or a server."
 has-permalinks: true
 tutorial:
   id: fetchdata
 next: forms/
 next-title: "Get Input from a Form"
-prev: futures/
-prev-title: "Use Future-Based APIs"
+prev: cmdline/
+prev-title: "Write Command-Line Apps"
 ---
 
 {% capture whats_the_point %}
 
 * Data on the web is often formatted in JSON.
 * JSON is text based and human readable.
 * The dart:convert library provides support for JSON.
 * Use HttpRequest to dynamically load data.
 
 {% endcapture %}
@@ skipping 455 matching lines @@
 * The next tutorial,
 [Get Input from a Form](/docs/tutorials/forms/),
 contains a client/server example that
 shows you how to use a form to get data from the user,
 and using JSON, send that form to a server,
 and handle the server's response.
 
 {% endcapture %}
 
 {% include tutorial.html %}