Compatibility with json_serializable

Hi, thank you for your work on `tuple`!
Is there a recommended way to use `tuple` together with `json_serializable`?

For example, if I want to automatically serialize a class that looks like this:
```dart
@JsonSerializable(nullable: false)
class Person {
final String firstName;
final String lastName;
final Tuple2 myTuple;

Person({this.firstName, this.lastName, this.myTuple});

factory Person.fromJson(Map json) => _$PersonFromJson(json);
Map toJson() => _$PersonToJson(this);
}
```