Fixed deadlock in daily_file_sink that happened while cleaning older files. Thanks @IIFE for reporting(#1570) and for fixing(#1571).

Fixed ringbuffer_sink::last_raw() and ringbuffer_sink::last_formatted() that didn't return latest elements. Thanks @vekkuli for reporting and fixing (#1563).

Fixed missing symbol wstr_to_utf8buf(..) in windows dll build. Thanks @haquocviet for reporting (#1569).

Bumped bundled fmt to version 6.2.1.