Make `#[derive(Copy)]` enough for both `Clone` and `Copy`

To me it sounds like solving the "I don't like writing Clone," with an over-complicated solution which has a high chance of false-positives and/or significant performance regressions. Also becoming a potential SemVer hazard and taking from Rust's intentional explicitness.

Also, can't this be implemented as an external crate with some #[derive(Clopy)] to explore the actual usefulness for the ecosystem?