[Feature Request] RAHasher chd parent support

[Deide]

When calculating the hash of a chd with a parent, we get

chd_open failed: requires parent
Could not open track

But I see no way to provide a parent, and emulators just read the parent automatically.

I find the parent-child relationship useful to keep the original while being able to patch for undubs, mods and translations to roms/discs, and maybe only taking up an additional dozen megabytes as the child instead of duplicating another few gigabytes of data.