Support for complex (non-String) JSON keys

[gcameo]

At the moment, MapDeserializer throws an error if the key for the Map is not a String. Can we add a feature to allow the JSONConfig to have a custom deserializer for the Key, like in Jackson? Or Can we extend the Deserializer framework to allow registering custom Deserializers for a Map? At the moment, Deserializers can be registered for other datatypes through Adapters but not for a Map.

[rmannibucau]

don't think it is forbidden in the spec to register JSON-B components, can it be a yasson error?