[boost] [gil] Phasing out support C++11 and switching to C++17

Hi, We're discussing [1] to start switching GIL to C++17 in the near future and, following Peter Dimov's policy on phasing out C++XY support [2], we'd like to: 1. Declare C++11 support deprecated in 1.75 (December 2020) 2. Drop C++11 support in 1.77 (?) (August 2021) Could anyone help us validate and confirm that it's a good plan or are we overlooking any policies from Boost's release perspective? [1] https://lists.boost.org/boost-gil/2020/10/0465.php [2] https://pdimov.github.io/articles/phasing_out_cxx03.html Best regards, -- Mateusz Loskot, http://mateusz.loskot.net