im::Vector :: tail/init

https://docs.rs/im/10.0.0/im/vector/struct.Vector.html has tail/init, where

tail = stuff except for front
init = stuff except for back

This appears to have been removed from the latest: https://docs.rs/im/15.0.0/im/vector/struct.Vector.html

Question: Was this renamed? If it was removed, was there a rationale ?

The changelog says it was removed in version 11.0 (July 2018). The implementation changed in the same release. If you want the rationale beyond that, I'd contact the maintainer(s).