Add a predefined macro that is always the directory that limine.conf was loaded from?

I was thinking this might be a useful feature to have since I often found myself putting my `limine.conf` in the same parent directory as my boot files. The macro could be named `CONFIG_DIR` and would expand to a string suitable for use for loading kernels, modules, etc, from relative to the directory `limine.conf` was loaded from. Thoughts?