Macro impl_partial_eq

macro_rules! impl_partial_eq {
    (<I> $a:ty = $b:ty) => { ... };
    (<I, B> $a:ty = $b:ty) => { ... };
    (<$lt:lifetime, I> $a:ty = $b:ty) => { ... };
    (<$lt:lifetime, I, B> $a:ty = $b:ty) => { ... };
}