Add SDL2pp wrapper for optional

With future C++ standards, library will switch to std::optional, however
for now we need a wrapper to choose between our bundled implementation,
std::experimental::optional (if that's available) and std::optional
(when that's available)

SDL2pp/Optional.hh

@@ -0,0 +1,38 @@
+/*
+  libSDL2pp - C++11 bindings/wrapper for SDL2
+  Copyright (C) 2014 Dmitry Marakasov <amdmi3@amdmi3.ru>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef SDL2PP_OPTIONAL_HH
+#define SDL2PP_OPTIONAL_HH
+
+#include <SDL2pp/libcpp_optional.hh>
+
+namespace SDL2pp {
+
+template<typename T>
+using Optional = sdl2pp_libcpp_optional::optional<T>;
+
+using BadOptionalAccess = sdl2pp_libcpp_optional::bad_optional_access;
+
+constexpr sdl2pp_libcpp_optional::nullopt_t NullOpt = sdl2pp_libcpp_optional::nullopt;
+
+}
+
+#endif