externals: Update boost to 1.72 and add Boost Context

boost/algorithm/string/predicate_facade.hpp

@@ -0,0 +1,42 @@
+//  Boost string_algo library predicate_facade.hpp header file  ---------------------------//
+
+//  Copyright Pavol Droba 2002-2003.
+//
+// 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)
+
+//  See http://www.boost.org/ for updates, documentation, and revision history.
+
+#ifndef BOOST_STRING_PREDICATE_FACADE_HPP
+#define BOOST_STRING_PREDICATE_FACADE_HPP
+
+#include <boost/algorithm/string/config.hpp>
+
+/*
+ \file boost/algorith/string/predicate_facade.hpp
+ This file contains predicate_facade definition. This template class is used
+ to identify classification predicates, so they can be combined using
+ composition operators.
+*/
+
+namespace boost {
+    namespace algorithm {
+
+//  predicate facade ------------------------------------------------------//
+
+        //! Predicate facade
+        /*!
+            This class allows to recognize classification
+            predicates, so that they can be combined using
+            composition operators.
+            Every classification predicate must be derived from this class.
+        */
+        template<typename Derived>
+        struct predicate_facade {};
+
+    } // namespace algorithm
+} // namespace boost
+
+
+#endif  // BOOST_STRING_CLASSIFICATION_DETAIL_HPP