Use intra-doc links for `core/src/slice.mod.rs`
Use intra-doc links for `core/src/slice.mod.rs`

- most are using primitive types links, which cannot be used with intra
  links at the moment
- also `std` cannot be referenced in any link

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust