Issue 6626 - Document the rewrite filter option

pages/filters.html

Index: pages/filters.html
===================================================================
--- a/pages/filters.html
+++ b/pages/filters.html
@@ -176,16 +176,19 @@
       {{s75 <code><fix>donottrack</fix></code> — for any address matching a blocking rule with
       this option and not matching any exception rules with this option a
       <a href="http://donottrack.us/">Do-Not-Track header</a> will be sent (requires
       Adblock Plus 1.3.5 or higher).}} {{s76 For backwards compatibility it is recommended
       to use this option in combination with contradicting type options, this will prevent this
       filter from blocking anything in earlier Adblock Plus versions:
       <code><fix>*$donottrack,image,~image</fix></code>}}
     </li>
+    <li>
+      {{rewriteoption Rewrite the URL with the option <code><fix>rewrite=</fix></code>. You must use a regular expression filter, using <code><fix>$n</fix></code> in the rewrite argument, with n an number between 1 and 100, will insert the n-th parenthesis submatch of the filter. Anything not explicitely matched by the regular expression will be added in the rewritten string. For example <code><fix>/(server.com\/assets\/file.php)\?.*$/$rewrite=$1</fix></code> will rewrite the URL by removing everything that comes after ".php". If there is no query parameter (i.e. no '?'), this filter won't match. The rewrite parameter us the same syntax as JavaScript <code><fix>String.prototype.replace()</fix></code> when using a regular expression instead of a substring.}}

[Sebastian Noack, 2018/05/05 14:48:37]

I rather review larger texts with Google Docs:
https://docs.google.com/document/d/1OoXfJ3ZHpXxv5VXvIoovwefEMOXmRBYd-yYdPAJ2f...

[Sebastian Noack, 2018/05/08 06:32:23]

The edited version in the Google Doc looks good to me. But Manish probably
should have a look too.

[hub, 2018/05/08 13:36:11]

Done.

+    </li>
   </ul>
 
   <h4 id="regexps">{{s77 Using regular expressions}}</h4>
 
   <p>{{s79 If you want even more control about what your filters match and what they don't match, you can use regular expressions. For example the filter <code><fix>/banner\d+/</fix></code> will match <code><fix>banner123</fix></code> and <code><fix>banner321</fix></code> but not <code><fix>banners</fix></code>. You can check out <a href="{{s79-link https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Regular_Expressions#Writing_a_Regular_Expression_Pattern}}">documentation on regular expressions</a> to learn how to write them.}}</p>
 
   <p>{{s80 <em>Note</em>: For performance reasons it is recommended not to use regular expressions if they can be avoided.}}</p>