Revert "Ignore project files generated by IntelliJ IDEA"
Revert "Ignore project files generated by IntelliJ IDEA"

Curious other files like this won't be in the .gitignore. There's
a personal non-tracked git ignore file for those.

This reverts commit f4be9bf271362858619680c7b00a3b702e8f0f16.

imp/rust-itertools,rust-itertools/itertools