Mention in the exact_chunks docs that this can often be optimized better by the compiler

And also link from the normal chunks iterator to the exact_chunks one.

Author: sdroege

src/liballoc/slice.rs

@@ -613,6 +613,9 @@ impl<T> [T] {
     /// not divide the length of the slice, then the last chunk will
     /// not have length `chunk_size`.
     ///
+    /// See [`exact_chunks`] for a variant of this iterator that returns chunks
+    /// of always exactly `chunk_size` elements.
+    ///
     /// # Panics
     ///
     /// Panics if `chunk_size` is 0.
@@ -638,6 +641,10 @@ impl<T> [T] {
     /// not divide the length of the slice, then the last up to `chunk_size-1`
     /// elements will be omitted.
     ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler
+    /// can often optimize the resulting code better than in the case of
+    /// [`chunks`].
+    ///
     /// # Panics
     ///
     /// Panics if `chunk_size` is 0.
@@ -664,6 +671,9 @@ impl<T> [T] {
     /// not divide the length of the slice, then the last chunk will not
     /// have length `chunk_size`.
     ///
+    /// See [`exact_chunks_mut`] for a variant of this iterator that returns chunks
+    /// of always exactly `chunk_size` elements.
+    ///
     /// # Panics
     ///
     /// Panics if `chunk_size` is 0.
@@ -693,6 +703,11 @@ impl<T> [T] {
     /// not divide the length of the slice, then the last up to `chunk_size-1`
     /// elements will be omitted.
     ///
+    ///
+    /// Due to each chunk having exactly `chunk_size` elements, the compiler
+    /// can often optimize the resulting code better than in the case of
+    /// [`chunks_mut`].
+    ///
     /// # Panics
     ///
     /// Panics if `chunk_size` is 0.