Merge branch 'deepchem:master' into bert_to_merge

  - [ ] Run `yapf -i <modified file>` and check no errors (**yapf version must be  0.22.0**)

  - [ ] Run `mypy -p deepchem` and check no errors

  - [ ] Run `flake8 <modified file> --count` and check no errors

  - [ ] Run `python -m doctest <modified file>` and check no errors

- [ ] I have performed a self-review of my own code

- [ ] I have commented my code, particularly in hard-to-understand areas

- [ ] I have made corresponding changes to the documentation

After working through the tutorials, you can also go through other [examples](https://github.com/deepchem/deepchem/tree/master/examples). To apply `deepchem` to a new problem, try starting from one of the existing examples or tutorials and modifying it step by step to work with your new use-case. If you have questions or comments you can raise them on our [gitter](https://gitter.im/deepchem/Lobby).

### Supported Integrations

- [Weights & Biases](https://docs.wandb.ai/guides/integrations/other/deepchem): Track your DeepChem model's training and evaluation metrics.

### Gitter

Join us on gitter at [https://gitter.im/deepchem/Lobby](https://gitter.im/deepchem/Lobby). Probably the easiest place to ask simple questions or float requests for new features.

  def __init__(self,

               name: Optional[str] = None,

               entity: Optional[str] = None,

               project: Optional[str] = None,

               save_dir: Optional[str] = None,

               project: Optional[str] = "deepchem",

               mode: Optional[str] = "online",

               id: Optional[str] = None,

               resume: Optional[Union[bool, str]] = None,

      an entity is a username or team name where you're sending the W&B run

    project: str

      the name of the project where you're sending the new W&B run

    save_dir: str

      path where data is saved (wandb dir by default)

    mode: str

      W&B online or offline mode

    id: str

          'Note: Model checkpoints will not be uploaded to W&B in offline mode.\n'

          'Please set `mode="online"` if you need to log your model.')

    self.save_dir = save_dir

    self.save_run_history = save_run_history

    # set wandb init arguments

        entity=entity,

        mode=mode,

        id=id,

        dir=save_dir,

        resume=resume,

        anonymous=anonymous)

    self.wandb_init_params.update(**kwargs)

  flake8 <modified file> --count

If the command return 0, it means your code pass Flake8 check.

If the command returns 0, it means your code passes the Flake8 check.

Docstrings

----------

.. _`numpy`: https://numpydoc.readthedocs.io/en/latest/format.html#docstring-standard

All docstrings should follow the `numpy`_ docstring formatting conventions.

All docstrings should follow the `numpy`_ docstring formatting conventions. To

ensure that the code examples in the docstrings are working as expected, run

.. code-block:: bash

  python -m doctest <modified file>

Unit Tests

----------

make to the source code when you import the package and, in particular, it

allows you to import the new classes/methods for unit tests.

Ensure that the tests pass locally! Check this by running

.. code-block:: bash

  python -m pytest <modified file>

Testing Machine Learning Models

-------------------------------