Simplifying layer handling

      in_layers = [in_layers]

    tensors = []

    for input in in_layers:

      if isinstance(input, tf.Tensor):

        tensors.append(input)

      elif isinstance(input, tf.Variable):

        tensors.append(input)

      elif isinstance(input, Layer):

        tensors.append(input.out_tensor)

      else:

        raise ValueError('Unexpected input: ' + str(input))

      tensors.append(tf.convert_to_tensor(input))

    if reshape and len(tensors) > 1:

      shapes = [t.get_shape() for t in tensors]

      if any(s != shapes[0] for s in shapes[1:]):