Issue 6626 - Document the rewrite filter option

pages/filter-cheatsheet.html

Index: pages/filter-cheatsheet.html
===================================================================
--- a/pages/filter-cheatsheet.html
+++ b/pages/filter-cheatsheet.html
@@ -616,16 +616,23 @@
   <tr>
     <td><code>domain=</code></td>
     <td>{{s100 Specify a list of domains, separated by bar lines (|), on which a filter should be active. A filter may be prevented from being activated on a domain by preceding the domain name with a tilde (~).}}</td>
   </tr>
   <tr>
     <td><code>third-party</code><br><code>~third-party</code></td>
     <td>{{s101 Specify whether a filter should be active on third-party or first domains}}</td>
   </tr>
+  <tr>
+    <td colspan="2" style="text-align: center;">{{mischeader Misc}}</td>
+  </tr>
+  <tr>
+    <td><code>rewrite=</code></td>
+    <td>{{rewritedesc Specify a rewrite rule for the URL to be performed before downloading. The filter should be a regular expression. Use <code>$n</code> to insert submatches into the rewritten URL. See JavaScript own <code>String.prototype.replace()</code>.}}</td>

[Manish Jethani, 2018/05/10 02:47:39]

The filter can very well be a string. e.g. /foo^$rewrite=/bar

I think we should write this as "If the filter is a regular expression, use $n
to insert submatches ....".

[hub, 2018/05/15 17:47:50]

Done.

+  </tr>
 </table>
 
 <p>{{s102 Less frequently used options, including <code><fix>dtd</fix></code>, <code><fix>ping</fix></code>, <code><fix>xbl</fix></code>, <code><fix>xmlhttprequest</fix></code>, <code><fix>other</fix></code>, <code><fix>collapse</fix></code>, <code><fix>donottrack</fix></code> and <code><fix>match-case</fix></code> are explained in the <a href="https://adblockplus.org/en/filters#options">full documentation</a>.}}</p>
 
 <h2 id="elementhiding">{{s103 Element hiding}}</h2>
 
 <p>{{s104 It is generally recommended that users install the <a href="https://addons.mozilla.org/firefox/addon/elemhidehelper/">Element Hiding Helper for Adblock Plus</a> to assist them in the generation of  element hiding rules.}}</p>