Add option for renaming the .CHD > .CD1 .CD2 .CD3

Hi there, 

Would it be possible to add an option to rename the original CHD files to .CDX where X is disc number?

Its the recommended way of doing it for retropie so that they don't show up in emulation station...

https://retropie.org.uk/docs/Playstation-1/#m3u-playlists-for-cue-bins-or-chds
