title: WTForms - multi-value string to SelectMultipleField
body: <p>I have a WTForm called <code>TestForm</code> with the following property:</p>
  
  <pre><code>areas = SelectMultipleField(u'Test Areas', choices=TestArea.names())
  </code></pre>
  
  <p>When I create a new instance of <code>TestForm</code> and pass in an object with an <code>areas</code> property, the object doesn't have a list of values for <code>areas</code>, but rather a string with a value like <code>Area1;Area2;Area3</code>.  How can I go about translating between the list <code>['Area1', 'Area2', 'Area3']</code> that the <code>SelectMultipleField</code> expects, and the string that my object expects to find in <code>areas</code>?  I have several of these fields, so I would prefer not to have to pass in something like <code>TestForm(areas=myObj.areas.split(';'), field2=myObj.field2.split(';'), ..., myObj)</code>.</p>