Add tooltip viewport option, respect bounds of the viewport

docs/_includes/js/tooltips.html

@@ -134,6 +134,14 @@ $('#example').tooltip(options)
           <p>Appends the tooltip to a specific element. Example: <code>container: 'body'</code></p>
          </td>
        </tr>
+       <tr>
+         <td>viewport</td>
+         <td>string | object</td>
+         <td>{ selector: 'body', padding: 0 }</td>
+         <td>
+          <p>Keeps the tooltip within the bounds of this element. Example: <code>viewport: '#viewport'</code> or <code>{ selector: '#viewport', padding: 0 }</code></p>
+         </td>
+       </tr>
       </tbody>
     </table>
   </div><!-- /.table-responsive -->