[boost] Guidelines to implement Boost library evolution policy (was Boost 2.0)

The Boost Steering Committee set the overall policy for Boost library evolution to C++11, C++14, and beyond at its May 2014 meeting in Aspen. Guidelines to implement that policy are now available at https://svn.boost.org/trac/boost/wiki/BoostEvo The plan is to integrate these guidelines with similar material on the web site in time for the 1.56 release. --The Boost Steering Committee