In no particular order:
- Support "jku" / "x5u" (?)
- Support "zip" in JWS (after signature)
- Present key used for verification in result
- Refine crypto API to complete analogy to WebCrypto (with intelligent defaults)
- Support "zip"
- Support "crit"
- Add docstrings to polyfills.py
- Add docstrings to josecrypto.py
- Support "jwk"
- Support "x5c"
- Add tests for "jwk" and "x5c"
- Change unserialized format from base64 to binary
- Add Msgpack serialization
- Support "JWP" (or something for unsigned content)