Flask-jwt-extended

* Adds user_loader feature (49 and 56): Documentation here: http://flask-jwt-extended.readthedocs.io/en/latest/complex_objects_from_token.html

* Adds ability to overwrite expires time in create_access_token and create_refresh_token with optional expires_delta kwarg (52 and 55)

* Adds ability to get jti from an encoded token (51)
* New optional kwarg encoded_token which can be passed to get_stored_token (51)

* get_jwt_identity() now returns None instead of {} if no jwt is present

* Add jwt_optional decorator (46, thanks carlegbert)

* Fix import error when using older versions of pyjwt (refs 42)
* Make cryptography an optional dependency (see http://flask-jwt-extended.readthedocs.io/en/latest/installation.html for installation instructions)
* Add JWT_SECRET_KEY option. It will check this first, then fall back to using app.secret_key if it isn't set. Only used on symmetric signing algorithms, such as the HS* ones.
* Add JWT_PRIVATE_KEY option in place of app.secret_key for asymmetric (public/private key) signing algorithms. It now uses this option instead of app.secret_key, and is a breaking change from version 1.5.0.
* Update requirements.txt to use newest version of pyjwt