Fix some rustdoc warnings

Author: GuillaumeGomez

src/libstd/io/mod.rs

@@ -441,7 +441,7 @@ fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize>
 /// # }
 /// ```
 ///
-/// Read from `&str` because [`&[u8]`] implements `Read`:
+/// Read from [`&str`] because [`&[u8]`][slice] implements `Read`:
 ///
 /// ```
 /// # use std::io;
@@ -464,7 +464,8 @@ fn read_to_end<R: Read + ?Sized>(r: &mut R, buf: &mut Vec<u8>) -> Result<usize>
 /// [`File`]: ../fs/struct.File.html
 /// [`BufRead`]: trait.BufRead.html
 /// [`BufReader`]: struct.BufReader.html
-/// [`&[u8]`]: primitive.slice.html
+/// [`&str`]: ../../std/primitive.str.html
+/// [slice]: ../../std/primitive.slice.html
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(spotlight)]
 pub trait Read {