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

core/io/json.cpp

@@ -30,7 +30,7 @@
 
 #include "json.h"
 
-#include "core/print_string.h"
+#include "core/string/print_string.h"
 
 const char *JSON::tk_name[TK_MAX] = {
 	"'{'",