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

chrome/common/extensions/docs/templates/intros/permissions.html

 <p id="classSummary">
   Use the <code>chrome.permissions</code> module
   to implement optional permissions.
   As of Chrome 16, you can request optional permissions during your
   extension's regular application flow rather than at install time,
   so users understand why the permissions are needed
   and use only those that are necessary.
 </p>
 
 <p>
@@ skipping 40 matching lines @@
       present.
     </li>
   </ul>
 </p>
 
 
 <h3 id="manifest"> Step 2: Declare optional permissions in the manifest </h3>
 <p>
   Declare optional permissions in your <a href="manifest.html">extension
   manifest</a> with the <code>optional_permissions</code> key, using the
-  same format as the <a href="manifest.html#permissions">permissions</a>
+  same format as the <a href="declare_permissions.html">permissions</a>
   field:
 
 <pre>{
   "name": "My extension",
   ...
   <b>"optional_permissions": [ "tabs", "http://www.google.com/" ],</b>
   ...
 }</pre>
 </p>
 
@@ skipping 91 matching lines @@
   permissions: ['tabs'],
   origins: ['http://www.google.com/']
 }, function(removed) {
   if (removed) {
     // The permissions have been removed.
   } else {
     // The permissions have not been removed (e.g., you tried to remove
     // required permissions).
   }
 });
-</pre>
+</pre>