ThirdParty: Add optional-lite polyfill

Thanks to all who have made contributions to
https://github.com/martinmoene/optional-lite

include/icsneo/platform/optional.h

@@ -0,0 +1,23 @@
+#ifndef __ICSNEO_OPTIONAL_H_
+#define __ICSNEO_OPTIONAL_H_
+
+#include "nonstd/optional.hpp"
+
+/**
+ * We use icsneo::optional throughout the C++ API to allow for polyfilling
+ * std::optional into C++11 and C++14 environments. In a C++17 or better
+ * environment, icsneo::optional will be an alias of std::optional.
+ */
+
+namespace icsneo {
+
+	using nonstd::optional;
+	using nonstd::bad_optional_access;
+	using nonstd::make_optional;
+
+	using nonstd::nullopt;
+	using nonstd::nullopt_t;
+
+} // namespace icsneo
+
+#endif