externals: Update boost to 1.72 and add Boost Context

boost/safe_numerics/concept/numeric.hpp

@@ -1,29 +0,0 @@
-#ifndef BOOST_NUMERIC_CONCEPT_NUMERIC_HPP
-#define BOOST_NUMERIC_CONCEPT_NUMERIC_HPP
-
-//  Copyright (c) 2012 Robert Ramey
-//
-// Distributed under the Boost Software License, Version 1.0. (See
-// accompanying file LICENSE_1_0.txt or copy at
-// http://www.boost.org/LICENSE_1_0.txt)
-
-#include <limits>
-
-namespace boost {
-namespace safe_numerics {
-
-template<class T>
-struct Numeric {
-    // if your program traps here, you need to create a
-    // std::numeric_limits class for your type T.  see
-    // see C++ standard 18.3.2.2
-    static_assert(
-        std::numeric_limits<T>::is_specialized,
-        "std::numeric_limits<T> has not been specialized for this type"
-    );
-};
-
-} // safe_numerics
-} // boost
-
-#endif // BOOST_NUMERIC_CONCEPT_NUMERIC_HPP