title: Keras: Multiple Inputs for fit_generator using flow_from_directory
body: <p>Is it possible to have two flow_from_directory in a fit_generator?</p>
  
  <p>For example</p>
  
  <pre><code>train_generator_1 = train_datagen.flow_from_directory(
      train_data_dir_1,
      target_size=(img_height, img_width),
      batch_size=batch_size,
      class_mode='binary')
  
  train_generator_2 = train_datagen.flow_from_directory(
      train_data_dir_2,
      target_size=(img_height, img_width),
      batch_size=batch_size,
      class_mode='binary')
  
  custom_vgg_model.fit_generator(
      [train_generator_1, train_generator_2],
      steps_per_epoch=nb_train_samples,
      epochs=epochs,
      validation_data=validation_generator,
      validation_steps=nb_validation_samples,
      callbacks=[checkpointer, csv_logger])
  </code></pre>