[draft] Added support for quadrant chart

demos/index.html

@@ -54,6 +54,9 @@
       <li>
         <h2><a href="./pie.html">Pie</a></h2>
       </li>
+      <li>
+        <h2><a href="./quadrantchart.html">Quadrant charts</a></h2>
+      </li>
       <li>
         <h2><a href="./requirements.html">Requirements</a></h2>
       </li>