Rollup merge of #50588 - ExpHP:i-can-see-my-house-from-here, r=frewsxcv

Move "See also" disambiguation links for primitive types to top

Closes #50384.

<details>
<summary>Images</summary>

![rust-slice](https://user-images.githubusercontent.com/1411280/39843148-caa41c3e-53b7-11e8-8123-b57c25a4d9e0.png)

![rust-isize](https://user-images.githubusercontent.com/1411280/39843146-ca94b384-53b7-11e8-85f3-3f5e5d353a05.png)

</details>

r? @steveklabnik

src/liballoc/slice.rs

@@ -10,6 +10,8 @@
 
 //! A dynamically-sized view into a contiguous sequence, `[T]`.
 //!
+//! *[See also the slice primitive type](../../std/primitive.slice.html).*
+//!
 //! Slices are a view into a block of memory represented as a pointer and a
 //! length.
 //!
@@ -78,8 +80,6 @@
 //! * Further methods that return iterators are [`.split`], [`.splitn`],
 //!   [`.chunks`], [`.windows`] and more.
 //!
-//! *[See also the slice primitive type](../../std/primitive.slice.html).*
-//!
 //! [`Clone`]: ../../std/clone/trait.Clone.html
 //! [`Eq`]: ../../std/cmp/trait.Eq.html
 //! [`Ord`]: ../../std/cmp/trait.Ord.html

src/liballoc/str.rs

@@ -10,6 +10,8 @@
 
 //! Unicode string slices.
 //!
+//! *[See also the `str` primitive type](../../std/primitive.str.html).*
+//!
 //! The `&str` type is one of the two main string types, the other being `String`.
 //! Unlike its `String` counterpart, its contents are borrowed.
 //!
@@ -29,8 +31,6 @@
 //! ```
 //! let hello_world: &'static str = "Hello, world!";
 //! ```
-//!
-//! *[See also the `str` primitive type](../../std/primitive.str.html).*
 
 #![stable(feature = "rust1", since = "1.0.0")]