Support approx?

It would be nice to have support for the traits defined in [approx](https://crates.io/crates/approx), e.g., [`RelativeEq<_>`](https://docs.rs/approx/latest/approx/trait.RelativeEq.html),

```
the trait bound `ordered_float::NotNan<f64>: RelativeEq<_>` is not satisfied
```