Add make_void and void_t traits

doc/make_void.qbk

@@ -0,0 +1,47 @@
+[/
+Copyright 2017 Glen Joseph Fernandes
+<glenjofe -at- gmail.com>
+
+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).
+]
+
+[section:make_void make_void]
+
+    template<class...>
+    struct make_void
+    {
+        typedef void type;
+    };
+
+    template<class... Ts>
+    using void_t = typename make_void<Ts...>::type;
+
+__type The type `void` for all `T`.
+
+__header ` #include <boost/type_traits/make_void.hpp>` or ` #include <boost/type_traits.hpp>`
+
+[table Examples
+
+[[Expression] [Result Type]]
+
+[[`make_void<int>::type`][`void`]]
+
+[[`make_void<int&>::type`] [`void`]]
+
+[[`make_void<int(*)(int)>::type`] [`void`]]
+
+[[`make_void<int[]>::type`] [`void`]]
+
+[[`make_void<int[1]>::type`] [`void`]]
+
+[[`make_void<>::type`] [`void`]]
+
+[[`make_void<int, int>::type`] [`void`]]
+
+]
+
+[all_compilers]
+
+[endsect]

doc/type_traits.qbk

@@ -134,6 +134,7 @@
 
 [def __make_signed [link boost_typetraits.reference.make_signed make_signed]]
 [def __make_unsigned [link boost_typetraits.reference.make_unsigned make_unsigned]]
+[def __make_void [link boost_typetraits.reference.make_void make_void]]
 [def __decay [link boost_typetraits.reference.decay decay]]
 [def __is_complex [link boost_typetraits.reference.is_complex is_complex]]
 
@@ -316,6 +317,7 @@ See __has_trivial_constructor.
 
 [include make_signed.qbk]
 [include make_unsigned.qbk]
+[include make_void.qbk]
 
 [include promote.qbk]
 [include rank.qbk]