Concurrency -> Improved cxx::latch class.
Concurrency -> Improved cxx::latch class.

 - added missing acquire memory fence required,
   when cxx::latch::arrive() has just opened a cxx::latch

 - refactored cxx::latch::arrive_and_wait()
   to no longer perform unnecessary std::atomic::load()

 - adjusted maximum value of cxx::latch internal counter

mtezych/cpp,mtezych/cpp,mtezych/cpp,mtezych/cpp,mtezych/cpp