Compatibility with TensorFlow 2.4.1

[fracpete]

trafficstars

• Under TF 2, the output for the first checkpoint is .00001.index and .00001.data-00000-of-00001 rather than .0. get_epoch_number_from_path now strips path using os.path.basename and the .index suffix to properly return the number of the checkpoint.

• model_from_checkpoint_path now uses os.path.join to avoid having to supply a trailing slash for the model directory.