Add 1-indexed version of ${playlist-pos} property

[ghost]

Unless I am missing something, there's no sane way to have a term-status-msg that displays playlist position in a way that makes sense to humans. I would like to have my status line say something like file 3 of 5, but since there's no 1-indexed version of ${playlist-pos} I have to go for the much less intuitive playlist index: 2, playlist length: 5. Would it be possible to add a property like ${playlist-pos-1} or such?