an animation effect that shows a phantom that moves $from to $to.

tween.coffee

  tween = ($from, $to, therefore) ->
    $a = $from.clone()
    $from.css(opacity: 0.75)
    $a.css(position: 'absolute')
      .css($from.offset())
      .css('border-color', 'transparent')
    $from.parent().append $a
    $a.animate $to.position(),
       complete: ->
          $a.remove()
          $from.css(opacity: 1)
          do therefore