[boost] Twenty years and time to retire

The idea behind Boost was hatched in March, 1998, and the proposal document https://www.boost.org/users/proposal.pdf was released May 6, 1998. That makes Boost twenty years old, and makes me twenty years older. It is high time I retire from Boost; I haven't been able to contribute for some time now. Thanks to all of you who made Boost such an overwhelming success in the past and will drive Boost forward into a bright future! --Beman