docstr: returns a tensorflow flatten layer
  :param input_layer: previous layer
  :return: flatten layer
docstr_tok: ["returns","a","tensorflow","flatten","layer",":","param","input_layer",":","previous","layer",":","return",":","flatten","layer"]
code: def __call__(self, input_layer, **kwargs):
      """
      returns a tensorflow flatten layer
      :param input_layer: previous layer
      :return: flatten layer
      """
      return tf.contrib.layers.flatten(input_layer)
  
imports: import math
  from types import FunctionType
  import tensorflow
  from rl_coach.architectures import layers
  from rl_coach.architectures.tensorflow_components import utils
label_desc: Use image node_id 2 for calling the Flatten obj's underlying member method code with example usage: obj.__call__(input_layer) and returns: tf