v0.10.0

 -  0.10.0 (2020-05-04)
     *  Add `json.marshal` builtin function.
     *  Fix isssue where `{}` was treated as an empty set, not an empty object.
     *  Add `base64` builtin functions:

         -  `base64.encode`
         -  `base64.decode`
         -  `base64url.encode`
         -  `base64url.decode`
     *  Add `io.jwt` builtin functions:

         -  `io.jwt.encode_sign`
         -  `io.jwt.decode`
         -  `io.jwt.decode_verify`

        These use an external library and will not work for all key types.  We
        can resolve that as demand for other key types comes up.