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

servers/rendering/rasterizer.cpp

@@ -31,7 +31,7 @@
 #include "rasterizer.h"
 
 #include "core/os/os.h"
-#include "core/print_string.h"
+#include "core/string/print_string.h"
 
 Rasterizer *(*Rasterizer::_create_func)() = nullptr;