[boost] [Containers] String performance and compatibility

Hi Ion, I see that your string implementation has a small buffer optimisation (SBO). Have you tried to benchmark this, and/or any of the other design decisions? I vaguely recall that libc++ may have done some measurements but I can't find anything now. Also, have you considered adding e.g. a ctor that takes a std::string, for interoperability? (I guess the same could be asked for the other types.) Phil.