add parametric equations for eptrochoid

docs/build/html/genindex.html

@@ -125,6 +125,8 @@
       <li><a href="date.html#date.easter_monday">easter_monday() (in module date)</a>
 </li>
       <li><a href="date.html#date.easter_sunday">easter_sunday() (in module date)</a>
+</li>
+      <li><a href="function.html#function.epitrochoid">epitrochoid() (in module function)</a>
 </li>
   </ul></td>
 </tr></table>