wip/boost-mp11 20170622 NetBSD

Mp11 is a C++11 metaprogramming library based on template aliases and variadic templates. It implements the approach outlined in the article "Simple C++11 metaprogramming" and its sequel:

• http://pdimov.com/cpp2/simple_cxx11_metaprogramming.html
• http://pdimov.com/cpp2/simple_cxx11_metaprogramming_2.html

Reading these articles before proceeding with the documentation is _highly_ recommended.

The library is intended to be placed in a subdirectory `libs/mp11` in a Boost distribution, but can also be used standalone, although it does require Boost.Config. A single-header form is available in include/boost/mp11_single.hpp.