Flask-easyjwt

* `[fixed]` Dependencies in `setup.py`.

* `[fixed]` Updated dependency of EasyJWT.

* `[added]` Method `get_validity()` to return the validity of a token.

* Initial release of Flask-EasyJWT
* `[added]` Support defining the token key in the Flask application configuration (`EASYJWT_KEY`).
* `[added]` Support defining the token validity in the Flask application configuration (`EASYJWT_TOKEN_VALIDITY`).