Reduce macro spam in docs

## How can Bevy's documentation be improved?

Several of our macro-generated trait impls (e.g. [WorldQuery](https://docs.rs/bevy/0.5.0/bevy/ecs/query/trait.WorldQuery.html)) are flooded with near duplicate implementations that make it hard to browse. This is a workaround the lack of variadic generics, but we should try to reduce the end user impact.

We should be able to hide this with `#[doc(hidden)]`. Ideally, we get clever with our macro and hide all-but-one of the impls of each relevant type.