title: Jekyll - generating JSON files alongside the HTML files
body: <p>I'd like to make Jekyll create an HTML file and a JSON file for each page and post. This is to offer a JSON API of my Jekyll blog - e.g. a post can be accessed either at <code>/posts/2012/01/01/my-post.html</code> or <code>/posts/2012/01/01/my-post.json</code></p>
  
  <p>Does anyone know if there's a Jekyll plugin, or how I would begin to write such a plugin, to generate two sets of files side-by-side?</p>