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

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

 <h1>Other Deployment Options</h1>
 
 
 <p>
 Usually, users install their own extensions.
 But sometimes you might want an extension
 to be installed automatically.
 Here are two typical cases:
 </p>
 
@@ skipping 20 matching lines @@
 
 <ul>
   <li> Using a preferences JSON file </li>
   <li> Using the Windows registry (Windows only) </li>
 </ul>
 
 <p>
 Both ways support installing an extension from a <code>.crx</code> extension
 file on the user's computer.  The preferences JSON file also supports installing
 an extension hosted at an
-<a href="autoupdate.html#H2-1">update URL</a>.
+<a href="autoupdate.html#update_url">update URL</a>.
 See <a href="hosting.html">hosting</a> for details on hosting an extension.
 </p>
 
 <h2 id="prereqs">Before you begin</h2>
 
 <p>
 First, package a
 <a href="packaging.html"><code>.crx</code> file</a>
 and make sure that it installs successfully.
 </p>
 <p>
 If you wish to install from an
- <a href="autoupdate.html#H2-1">update URL</a>, ensure that the extension
+ <a href="autoupdate.html#update_url">update URL</a>, ensure that the extension
 is properly <a href="hosting.html">hosted</a>.
 </p>
 
 <p>
 Then, before you edit the preferences file or the registry,
 make a note of the following:
 </p>
 
 <ul>
  <li> The intended <b>location</b> of the extension's <code>.crx</code> file,
@@ skipping 183 matching lines @@
 <p>
 This section answers common questions about external extensions.
 </p>
 
 <br>
 
 <p><b>Can I specify a URL as a path to the external extension?</b> </p>
 <p>Yes, if you use a <a href="#preferences">preferences JSON</a> file. The
 extension must be hosted as explained in <a href="hosting.html">hosting</a>.
 Use the "external_update_url" property to point to an
-<a href="autoupdate.html#H2-2">update manifest</a> that has the URL for your
+<a href="autoupdate.html#update_manifest">update manifest</a> that has the URL for your
 extension.</p>
 
 <br>
 
 <p><b>What are some common mistakes when installing with the preferences
 file?</b></p>
 <ul>
   <li>
     Not specifying the same id/version
     as the one listed in the <code>.crx</code> </li>
@@ skipping 35 matching lines @@
 external extension is blacklisted. </p>
 
 <br>
 
 <p><b>How do I get off the blacklist?</b> </p>
 <p>If the user uninstalls your extension, you should respect that
 decision. However, if you (the developer) accidentally uninstalled
 your extension through the UI,
 you can remove the blacklist tag
 by installing the extension normally
-through the UI, and then uninstalling it. </p>
+through the UI, and then uninstalling it. </p>