Document switch to mulxp1_hash

doc/hash/recent.adoc

@@ -13,6 +13,9 @@ https://www.boost.org/LICENSE_1_0.txt
 * Added an overload of `hash_value` for `std::nullptr_t`.
 * Added `is_tuple_like` and an overload of `hash_value` for
   tuple-like types.
+* Changed string hashing to use
+  https://github.com/pdimov/mulxp_hash[`mulxp1_hash`]. This
+  improves both quality and speed.
 
 == Boost 1.81.0
 

doc/hash/reference.adoc

@@ -242,11 +242,16 @@ for( ; first != last; ++first )
 }
 ----
 
-Otherwise, bytes from `[first, last)` are coalesced in an unspecified manner
-and then passed to `hash_combine`, more than one at a time. This is done in
-order to improve performance when hashing strings.
+Otherwise, bytes from `[first, last)` are coalesced and hashed in an
+unspecified manner. This is done in order to improve performance when hashing
+strings.
 --
 
+Remarks: ::
+  For chars, the current implementation uses
+  https://github.com/pdimov/mulxp_hash[`mulxp1_hash`] when `std::size_t` is
+  64 bit, and `mulxp1_hash32` when it's 32 bit.
+
 [source]
 ----
 template<class It> std::size_t hash_range( It first, It last );