added epub support

Author: mosabua

site/index.html

@@ -12,6 +12,7 @@ <h1>The Hudson Book</h1>
   <li><a href="book-hudson.html">One large html page</a></li>
   <li><a href="book-hudson.chunked/index.html">Multiple html pages</a></li>
   <li><a href="book-hudson.pdf">PDF</a></li>
+  <li><a href="book-hudson.epub">epub</a></li>
   <li><a href="the-hudson-book.tar.gz">All together in an archive<a/></li>
 </ul>
 <div xmlns:cc="http://creativecommons.org/ns#"