Allow audience & issuer to be specified

👋 Hey,

When decoding a JWT, I need to specify an audience and issuer.
Currently I get 
```
Wrong token: Invalid audience
```

Looking at the code there's no way to pass in the intended audience or issuer.

with `jose` I would do
```python
decoded = jwt.decode(token, public_key, algorithms=[alg], audience=aud, issuer=issuer)
```