Modify so that niflib compiles as it points to the correct enum file.

niflib.h

@@ -51,7 +51,7 @@ POSSIBILITY OF SUCH DAMAGE. */
 #include "nif_math.h"
 #include "nif_versions.h"
 #include "Ref.h"
-#include "nif_enums.h"
+#include "gen/enums.h"
 
 using namespace std;
 namespace Niflib {