v.1.6.0
The v.1.6.0 of so5extra has been adapted to changes in SObjectizer-5.8.0.
NOTE: so5extra-1.6.0 requires SObjectizer-5.8.0 and can't be used with previous versions of the SObjectizer Core.
The unique_subscribers mbox is now a part of SObjectizer-5.8. The header file so_5_extra/mboxes/unique_subscribers.hpp and the function so_5::extra::mboxes::unique_subscribers::make_mbox are kept just for compatibility reasons.
Asio updated to v.1.28.0, doctest updated to v.2.4.8.