Reorganized core/ directory, it was too fatty already

-Removed FuncRef, since Callable makes it obsolete
-Removed int_types.h as its obsolete in c++11+
-Changed color names code

modules/xatlas_unwrap/register_types.cpp

@@ -30,7 +30,7 @@
 
 #include "register_types.h"
 
-#include "core/error_macros.h"
+#include "core/error/error_macros.h"
 
 #include "core/crypto/crypto_core.h"