Code style standardization

Create standard to define new PRs and commit.

We have many case like that:
https://github.com/flask-extensions/Flask-GoogleMaps/blob/f9e55917a3cbb98199e5a0cc4bc7a4745b68dd46/flask_googlemaps/__init__.py#L223-L234

What the form is more correctly or preferable for this project?

I think the best way is to use the [Black](https://black.readthedocs.io/en/stable/index.html#) and respect [PEP-8](https://www.python.org/dev/peps/pep-0008/) using `black -l 80`

Maybe add `-s` flag to not normalize strings.

Another case is related to docstring standards:
https://github.com/flask-extensions/Flask-GoogleMaps/blob/f9e55917a3cbb98199e5a0cc4bc7a4745b68dd46/flask_googlemaps/__init__.py#L46

In some docstrings we have parameters explanations in others not. In another cases we has things that can be replaced by type annotations
https://github.com/flask-extensions/Flask-GoogleMaps/blob/f9e55917a3cbb98199e5a0cc4bc7a4745b68dd46/flask_googlemaps/__init__.py#L421-L428

We can test it in a CI using tox, or not, is only a sugestion