macaroon_deserialize_json is not declared in macaroons.h

[rogpeppe]

There is a macaroon_serialize_json function, but no macaroon_deserialize_json function.

[rogpeppe]

Oops, my mistake. It is just not mentioned in the macaroons.h file. That's still an issue though.

[rescrv]

The JSON format is not yet stabilized, so we didn't (fully) expose the functions to work with it.