[boost] The deadline for new libraries and breaking changes in Boost 1.78.0 is Friday, October 29

Sorry for the late notice; the deadline was supposed to be today, but I'm extending it to Friday. See https://www.boost.org/development/index.html https://www.boost.org/development/index.html for the full calendar Next deadline: Boost 1.78.0 closed for beta Wednesday, Nov 3, 2021 — The Release Managers