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

drivers/unix/file_access_unix.cpp

@@ -33,7 +33,7 @@
 #if defined(UNIX_ENABLED) || defined(LIBC_FILEIO_ENABLED)
 
 #include "core/os/os.h"
-#include "core/print_string.h"
+#include "core/string/print_string.h"
 
 #include <sys/stat.h>
 #include <sys/types.h>