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/math/aabb.cpp

@@ -30,8 +30,8 @@
 
 #include "aabb.h"
 
-#include "core/print_string.h"
-#include "core/variant.h"
+#include "core/string/print_string.h"
+#include "core/variant/variant.h"
 
 real_t AABB::get_area() const {
 	return size.x * size.y * size.z;