autodict alternative generating a `to_dict()` or `as_dict()` method

[smarie]

@autodict currently makes the class behave as a dict so that all atributes can also be accessed as dict items.

• side remark: current implementation is maybe (?) overkill for non-slots classes where there is already a __dict__ inside. This is not really an issue for now
• some (most?) users might prefer to have a as_dict or to_dict method to convert the object