just added deferred support suggestestion for issue #45

I just implemented something to get me deferred-responses working. I am using it in my coffeescript application like this

```coffeescript
$.mockjax (settings) ->
  df = new $.Deferred()
  if settings.headers?['X-Amz-Target']
    serviceTarget = settings.headers['X-Amz-Target']
    console.log 'mocking service target:', serviceTarget
    targetFunction = serviceTarget.split('.').pop()
    window.charlie.service[targetFunction](settings.data)
      .done (result) =>
        df.resolve result
    return df
  else
    return

think this could be useful. if anybody is interested i would add some tests to it, so we can go further with this suggestion. what do you think?