Fix some typos, broken links and other issues in extension docs

chrome/common/extensions/docs/templates/articles/getstarted.html

 <h1>Getting Started: Building a Chrome Extension</h1>
 
 <p>
   Extensions allow you to add functionality to Chrome without diving deeply
   into native code. You can create new extensions for Chrome with those core
   technologies that you're already familiar with from web development: HTML,
   CSS, and JavaScript. If you've ever built a web page, you should feel right at
   home with extensions pretty quickly; we'll put that to the test right now by
   walking through the construction of a simple extension that will give you
   one-click access to pictures of kittens. Kittens!
@@ skipping 165 matching lines @@
       <img src="{{static}}/images/hotdogmenu.png"
            height="29"
            width="29"
            alt="The menu's icon is three horizontal bars.">. and
       select <strong>Extensions</strong> under the <strong>Tools</strong> menu
       to get to the same place).
     </p>
   </li>
   <li>
     <p>
-      Ensure that the <strong>Developer Mode</strong> checkbox in the top
+      Ensure that the <strong>Developer mode</strong> checkbox in the top
       right-hand corner is checked.
     </p>
   </li>
   <li>
     <p>
       Click <strong>Load unpacked extension&hellip;</strong> to pop up a
       file-selection dialog.
     </p>
   </li>
   <li>
@@ skipping 76 matching lines @@
       walk you through each API in turn.
     </p>
   </li>
   <li>
     <p>
       Finally, the <a href="devguide.html">developer's guide</a> has dozens of
       additional links to pieces of documentation you might be interested in.
     </p>
   </li>
 </ul>