[clojure mode] Enable editor features on demo page.

This PR enables the following editor features on the demo page
for Clojure mode:
- line numbers
- bracket matching
- bracket auto-closing

Author: finalfantasia

mode/clojure/index.html

@@ -6,6 +6,8 @@
 
 <link rel="stylesheet" href="../../lib/codemirror.css">
 <script src="../../lib/codemirror.js"></script>
+<script src="../../addon/edit/closebrackets.js"></script>
+<script src="../../addon/edit/matchbrackets.js"></script>
 <script src="clojure.js"></script>
 <style>.CodeMirror {background: #f8f8f8;}</style>
 <div id=nav>
@@ -83,7 +85,12 @@ <h2>Clojure mode</h2>
 
 </textarea></form>
     <script>
-      var editor = CodeMirror.fromTextArea(document.getElementById("code"), {});
+      var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
+          autoCloseBrackets: true,
+          lineNumbers: true,
+          matchBrackets: true,
+          mode: 'text/x-clojure'
+      });
     </script>
 
     <p><strong>MIME types defined:</strong> <code>text/x-clojure</code>.</p>