add extra linebreaks so rustdoc can identify the first sentence

there should probably be a lint against this in rustdoc, it causes
too many lines to be shown in the short documentation overviews

expecially noticable for the slice primative type:
https://doc.rust-lang.org/std/index.html

Author: lolbinarycat

Diff for: core/src/hint.rs

@@ -1,6 +1,7 @@
 #![stable(feature = "core_hint", since = "1.27.0")]
 
 //! Hints to compiler that affects how code should be emitted or optimized.
+//!
 //! Hints may be compile time or runtime.
 
 use crate::{intrinsics, ub_checks};

Diff for: core/src/primitive_docs.rs

@@ -832,8 +832,9 @@ mod prim_array {}
 #[doc(alias = "[")]
 #[doc(alias = "]")]
 #[doc(alias = "[]")]
-/// A dynamically-sized view into a contiguous sequence, `[T]`. Contiguous here
-/// means that elements are laid out so that every element is the same
+/// A dynamically-sized view into a contiguous sequence, `[T]`.
+///
+/// Contiguous here means that elements are laid out so that every element is the same
 /// distance from its neighbors.
 ///
 /// *[See also the `std::slice` module](crate::slice).*