title: upload file in ajax with wtforms
body: <p>I use wtforms to handle forms. so i create form like this:</p>
  
  <pre><code>class ProfileForm(Form):
      firstName = TextField(_('firstName'), [validators.Required(), validators.Length(min=3, max=45)])
      lastName = TextField(_('lastName'), [validators.Required(), validators.Length(min=3, max=45)])
      avatar = FileField(_('avatar'), [check_file])
  </code></pre>
  
  <p>this form work in simple upload fine ... but what about ajax ?</p>
  
  <p>is there any plugin to create iFrame or somethings to upload file via ajax? or i must handle this form in another way?</p>
  
  <p>ps: IE support be important </p>
  
  <p>ps2: i use wtform for another without file in ajax to. just by serialize form and submit it ... </p>