Flask Jwt Simple Versions Save

• Adds JWT_DECODE_AUDIENCE option (per #1)

• No longer returns the InvalidHeaderError handler if an authorization header appears in a different format then we expect in the @jwt_optional endpoint. (refs https://github.com/vimalloc/flask-jwt-extended/issues/82)
• Register this extension with a flask app in a more proper way

Initial release. This is basically a less opinionated and simpler version of my Flask-JWT-Extended extension, without all the extra features baked on top. It is perfect for fast prototyping if you aren't going to be using flask for your final product, or for building a flask app that can integrate with other JWT providers.