Implement convenience traits for encoded types

[george-hopkins]

Implement From<T> and Debug for Base64<T>, Json<T>, Msgpack<T> and Protobuf<T>

[zshipko]

Thanks! This is great as-is but I wonder if it makes sense to implement From<Json<T>> for T for encoding types also?

[george-hopkins]

Unfortunately, we can't implement From<Json<T>> on foreign types. We could implement Into<T> for Json<T> but this would prevent users from implementing From<Json<T>> themselves.