Basic autoencoder model.

def autoencoder_basic_discrete():
  """Basic autoencoder model."""
  hparams = autoencoder_autoregressive()
  hparams.num_hidden_layers = 5
  hparams.hidden_size = 64
  hparams.bottleneck_bits = 1024
  hparams.bottleneck_noise = 0.1
  hparams.add_hparam("discretize_warmup_steps", 16000)
  return hparams