Add a TFDS user CLI

It would be nice to have a user CLI which is installed at the same time as TFDS to pre-generate dataset:

tfds new my_dataset  # Generate the base template & cie
cd my_dataset/
tfds build  # Generate my_dataset

tfds new would create the following folder structure:

my_dataset/
    fake_data/
    __init__.py
    dataset.py
    dataset_test.py
    make_fake_data.py
    checksum.txt

Some technical details:

• Script would be implemented in python using argparse
• Is added through the entry_points={'command'} section in setup.py

This first require to implement the one folder==one dataset model.

[acharles7]

Thanks for letting me know, Let me know if you need any help:)

[vijayphoenix]

For future work, see https://github.com/tensorflow/datasets/issues/2447