[boost] What is status of Boost.Sync?

Hi, The library docs docs say it's been in Boost since 1.55. Boost master has no submodule for it. Boost develop has submodule for it If Sync was removed, why it is still in develop? If Sync was added, hence it is in develop, why the docs mention 1.55 and why it is not in master? What is the status of this thing? Best regards, -- Mateusz Loskot, http://mateusz.loskot.net