Feature request: index value formatting

[ruckmann]

Dear Simon,

late but very enthusiastic feed back from my side: I have just started a reorganization of my music collection. Making use of the IndexFormat feature, I am now able to structure my collection in a much better way eliminating lot of redundancy currently in. From all what I see, it works pretty fine. I am very happy benefitting from this feature and I am totally impressed about your speed coming up providing it. Thanks a lot!!!