Fix intra-doc links in `core`
Fix intra-doc links in `core`

Caught by my malformed generics diagnostics!

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