Simplify examples

src/io/read_exact.rs

@@ -16,9 +16,7 @@ use io::Read;
 /// use nb::io::read_exact;
 ///
 /// let source = [5, 6, 7];
-/// let reader = &mut &source[..];
-///
-/// let mut reading = read_exact(reader, [0, 0]);
+/// let mut reading = read_exact(&source[..], [0, 0]);
 /// let (_, buffer) = block!(reading.poll()).ok().unwrap();
 /// assert_eq!(buffer, [5, 6]);
 /// # }

src/io/write_all.rs

@@ -17,8 +17,7 @@ use io::Write;
 ///
 /// let mut buffer = [0; 3];
 /// {
-///     let writer = &mut buffer[..];
-///     let mut writing = write_all(writer, [5, 6]);
+///     let mut writing = write_all(&mut buffer[..], [5, 6]);
 ///     block!(writing.poll()).ok().unwrap();
 /// }
 /// assert_eq!(buffer, [5, 6, 0]);