size_t, more info

[Sylvain Bougerel]

> So, well, for the sake of portability, and yet to retain namespace
> scoping, we could:
>  namespace std
>  {
>      using ::ptrdiff_t;
>      using ::size_t;
>  }
> Just for about everything, which appears to work everywhere according
> to my understanding of boost code. Yet we can retain the use of
> std::size_t, to signify this comes for the standard header, and it's
> not something we've declared in our code.
>
> Voila.
>

Me again. We could put that in that file Paul created. May I suggest
the we rename the file to config.hpp and include the library version
number in it too?