title: Flatten batch in tensorflow
body: <p>I have an input to tensorflow of shape <code>[None, 9, 2]</code> (where the <code>None</code> is batch).</p>
  
  <p>To perform further actions (e.g. matmul) on it I need to transform it to <code>[None, 18]</code> shape. How to do it? </p>