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.

CMakeLists.txt

@@ -209,10 +209,6 @@ if(WIN32)
 	endif()
 endif(WIN32)
 
-# optional-lite
-add_subdirectory(third-party/optional-lite)
-target_link_libraries(icsneocpp PUBLIC optional-lite)
-
 if(${CMAKE_SYSTEM_NAME} STREQUAL "Darwin")
 	target_link_libraries(icsneocpp PUBLIC "-framework CoreFoundation" "-framework IOKit")
 endif()

include/icsneo/platform/optional.h

@@ -1,7 +1,7 @@
 #ifndef __ICSNEO_OPTIONAL_H_
 #define __ICSNEO_OPTIONAL_H_
 
-#include "nonstd/optional.hpp"
+#include "icsneo/third-party/optional-lite/include/nonstd/optional.hpp"
 
 /**
  * We use icsneo::optional throughout the C++ API to allow for polyfilling