title: leaflet + gMapCatcher- change zxy template
body: <p>I'm using <code>leaflet</code> with tiles generated by gMapCatcher.
  the file names there is totally different.
  For example - zoom level 17 in leaflet is level 0 at gMapCatcher.</p>
  
  <p>I need to change the url template </p>
  
  <pre><code>'http://{s}.somedomain.com/blabla/{z}/{x}/{y}.png'
  </code></pre>
  
  <p>so I can insert the calculations for the right directories </p>
  
  <p>I tried the naive way to write the calculations within the template but it does not work.</p>