[boost] [http] Boost.Http formal review is finished

The formal review of Boost.Http is finished, and I would like to thank all who participated. The following reviews have been recorded: - Antony Polukhin: No - Darren Cook: No - David Sankel: No - Lee Clagett: No - Niall Douglas: Yes, conditionally - Roland Bock: No - Tom Kent: No Please let me know if I have missed any. The final review results will be posted later.