Derives a quicker PartialOrd for types that already implement Ord.

```rust // Input

[derive(PartialEq, Eq, Ord, impartial_ord::ImpartialOrd)]

struct MyStruct;

// Output impl PartialOrd for MyStruct { #[inline] fn partial_cmp(&self, other: &Self) -> Option { Some(Ord::cmp(self, other)) } } ```