Exception when _process_event returns dict

[orestis]

This could be a documentation issue, or me not understanding how to use structlog, but here goes:

In BoundLoggerBase (_base.py), _process_event can either return a tuple of: (event_dict,), {} or just event_dict. However in the same class, _proxy_to_logger always calls _process_event like so:

            args, kw = self._process_event(method_name, event, event_kw)

I have a custom logger that needs access to the raw event_dict (to store it in a database), so I don't have a last processor to turn it into a string.

I have various workarounds I can think of (e.g. serialize the event_dict, and deserialize in the logger as needed), but I was wondering if this was a bug.