[*] Add append_to attribute

Add append_to attribute so this gem works with modal windows.
Example:
    <div class="form-group ui-widget" id="skill_autocomplete">
      <%= f.label :name, class: 'control-label' %><br>
      <%= f.autocomplete_field :name, autocomplete_skill_name_skills_path, {class: 'form-control', :append_to=> '#skill_autocomplete'} %>
    </div>