add new platform_abstraction

add support of loading ttf file

source/detail/platform_spec_selector.hpp

@@ -0,0 +1,21 @@
+/**
+ *	Selector of Platform Specification
+ *	Nana C++ Library(http://www.nanapro.org)
+ *	Copyright(C) 2003-2016 Jinhao(cnjinhao@hotmail.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)
+ *
+ *	@file nana/detail/platform_spec_selector.hpp
+ *
+ *	@brief Selects the proper platform_spec header file for the current platform
+ */
+
+#include <nana/config.hpp>
+
+#if defined(NANA_WINDOWS)
+#include "mswin/platform_spec.hpp"
+#elif defined(NANA_LINUX) || defined(NANA_MACOS)
+#include "posix/platform_spec.hpp"
+#endif