Specialized trait impls appear unannotated in the docs

[Nemo157]

Looking at the docs for ToString it shows that there's an implementation for char

impl ToString for char

but, this overlaps the blanket impl + char's Display impl:

impl<T> ToString for T where T: Display + ?Sized
impl Display for char

Showing this specialization-based implementation in the docs with no indication of why the overlap is allowed is confusing.

Since specialization is supposed to be generally invisible to the user, maybe we shouldn't be showing specialized impls at all.

[the8472]

The libs dev guide already recommends to hide specializations in private traits, that would also help this case.

https://std-dev-guide.rust-lang.org/code-considerations/using-unstable-lang/specialization.html

[steffahn]

Any reason not to simply add #[doc(hidden)] on all the specialized impls for now?