-type config() :: #{new_line => boolean(), new_line_type => nl | crlf | cr | unix | windows | macos9, key_mapping => #{atom() => atom()}, format_funs => #{atom() => fun((_) -> _)}}.
-spec format(logger:log_event(), config()) -> unicode:chardata().
-spec system_time_to_iso8601(integer()) -> binary().
-spec system_time_to_iso8601_nano(integer()) -> binary().