title: how to stack Vertically or Horizontally two MultiCheckboxField wtform fields
body: <p>i have a form that uses a widget. what i want is two vertical columns side by side with the checkboxes.</p>
  
  <pre><code>class MultiCheckboxField(SelectMultipleField):
      widget = widgets.ListWidget(prefix_label=False)
      option_widget = widgets.CheckboxInput()
  
  class SimpleForm2(Form):
      menu_items = MultiCheckboxField('Menu Item', choices=[], coerce=int)
      contents = MultiCheckboxField('Content', choices=[], coerce=int)
      submit = SubmitField('OK')
  </code></pre>
  
  <p>for example</p>
  
  <ul>
  <li>Menu Item | Content </li>
  <li>cbox1 | cbox1'</li>
  </ul>