Optional: Move optional-lite to the include/third-party directory

This fixes the use case of adding the include folder
manually to an outside project.

include/icsneo/third-party/optional-lite/example/05-no-exceptions.cpp

@@ -0,0 +1,13 @@
+#include "nonstd/optional.hpp"
+
+using nonstd::optional;
+
+int main()
+{
+    optional<int> v;
+
+    v.value();  // asserts (normally throws)
+}
+
+// cl -nologo -I../include 05-no-exceptions.cpp && 05-no-exceptions
+// g++ -Wall -fno-exceptions -I../include -o 05-no-exceptions 05-no-exceptions.cpp && 05-no-exceptions