To much String::clone()?

In src/value.rs (https://github.com/mehcode/config-rs/blob/master/src/value.rs#L148) we clone() a String. That leads to a lot of String cloning when using this library.

Yesterday, I played around with cargo-flamegraph and cargo-bench a bit because of this. I am by no means an expert on how to do performance analysis and these kind of things, but from what I could see, String::clone() is not insignificant in the runtime cost of this crate.
Maybe, and I want to empathize this, maybe we could gain a lot from removing this one clone() call.

BUT the problem is, that it is not simple! I tried a bit, and using a &'a str in this place would basically put a lifetime on everything in the crate.
In some places, it is not even possible to have a lifetime... maybe I should have invested more time to gain some results,... I am not sure.

Maybe someone else has an idea, or is better with driving such analysis...

Start in src/value.rs around line 148 and inspect how the cloned String flows through the crate. Use cargo-flamegraph and cargo-bench to measure whether this clone is a significant cost, then assess the lifetime implications of changing it. Done means having benchmark evidence and a tested, maintainable approach to reducing or retaining the clone.