`hex::FromHex::Error` does not implement `Eq`

[tcharding]

Is there some reason why FromHexError does not derive Eq? It seems common in the Rust std lib to do so, here are a bunch of example errors that do so: https://doc.rust-lang.org/std/cmp/trait.Eq.html

Happy to do a PR but its so trivial I thought there might be some reason I can't work out.

Thanks

[nouritsu]

Are there plans to work on this?