title: Beamsearch with alignment_history = True(attentionwrapper)
body: <p>tensorflow 1.9(and maybe some earlier versions) support using <code>BeamSearchDecoder</code> with the combination of <code>tf.contrib.seq2seq.AttentionWrapper</code> and its argument <code>alignment_history = True</code>. If using <code>BeamSearchDecoder</code>, output beams are ordered from best to worst. I want to know that if the <code>alignment_history</code> inside <code>AttentionWrapperState</code> is ordered or not.</p>
  
  <p>** I found that the shape of <code>alignment_history</code> is [decoder_timesteps, batch * beam_size, encoder_timesteps]</p>