Add use_default to Core

include/boost/core/use_default.hpp

@@ -0,0 +1,17 @@
+/*
+Copyright 2019 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#ifndef BOOST_CORE_USE_DEFAULT_HPP
+#define BOOST_CORE_USE_DEFAULT_HPP
+
+namespace boost {
+
+struct use_default { };
+
+} /* boost */
+
+#endif