Pairs !- tuples, so add some better Meta support

I usually use `tuple` for all product types, but some STL bits
use pair, which is a distinct type.  So here's some helpful
meta helpers for them.

Meta/is_pair.h

@@ -0,0 +1,33 @@
+static_assert( __cplusplus > 201700, "C++17 Required" );
+
+#pragma once
+
+#include <Alepha/Alepha.h>
+
+#include <type_traits>
+#include <utility>
+
+namespace Alepha::Hydrogen::Meta
+{
+	inline namespace exports { inline namespace type_traits {} }
+
+	namespace detail::type_traits::is_pair
+	{
+		inline namespace exports
+		{
+			template< typename T >
+			struct is_pair : std::false_type {};
+
+			template< typename ... Args >
+			struct is_pair< std::pair< Args... > > : std::true_type {};
+
+			template< typename T >
+			constexpr bool is_pair_v= is_pair< T >::value;
+		}
+	}
+
+	namespace exports::type_traits
+	{
+		using namespace detail::type_traits::is_pair::exports;
+	}
+}