Use static linking instead of dynamic linking

include/core/Plane.hpp

@@ -1,16 +1,6 @@
 #ifndef PLANE_H
 #define PLANE_H
 
-#if defined(_WIN32)
-#  ifdef _GD_CPP_CORE_API_IMPL
-#    define GD_CPP_CORE_API __declspec(dllexport)
-#  else
-#    define GD_CPP_CORE_API __declspec(dllimport)
-#  endif
-#else
-#  define GD_CPP_CORE_API
-#endif
-
 #include "Vector3.hpp"
 
 #include <cmath>
@@ -25,7 +15,7 @@ enum ClockDirection {
 	COUNTERCLOCKWISE
 };
 
-class GD_CPP_CORE_API Plane {
+class Plane {
 public:
 	Vector3 normal;
 	real_t d;