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

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

 <p>The downloads API allows you to programmatically initiate, monitor,
 manipulate, and search for downloads.</p>
 
 <h2 id='manifest'>Manifest</h2>
 
 <p> You must declare the 'downloads' permission in the <a
 href='manifest.html'>extension manifest</a> to use this API, along with <a
-href='manifest.html#permissions'>host permissions</a> for any hosts that you
+href='declare_permissions.html'>host permissions</a> for any hosts that you
 may pass to $ref:downloads.download.</p>
 
 <pre>{
   'name': 'My extension',
   ...
 <b>  'permissions': [
     'downloads',
     '*://*.google.com'
   ]</b>,
   ...
 }</pre>
 
 <p>If the URL's hostname is not specified in the permissions, then 
 $ref:downloads.download will call its callback with a null
 <code>downloadId</code> and set the 
 $ref:runtime.lastError
 object to indicate that the extension does not have permission to access that
 hostname.</p>
 
 <h2 id='examples'>Examples</h2>
 
 <p>You can find simple examples of using the downloads module in the <a
 href='http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/downloads/'>examples/api/downloads</a>
 directory. For other examples and for help in viewing the source code, see <a
-href='samples.html'>Samples</a>.</p>
+href='samples.html'>Samples</a>.</p>