title: tf.data.Dataset with constant size batches
body: <p>I have a dataset with 19 elements and a batch size of 10. I set my dataset to continuously iterate over the same elements but I noticed that the last batch has only 4 elements instead of 5, and then it starts over with 5, 5, 5, 4, and so on.</p>
  
  <p>How is is possible to force the iterator to fill up shorter batches with elements coming from the next iteration so that all the batches have the same size?</p>
  
  <p>P.S. just to understand, isn't this the obvious behavior when training a model?</p>