some "status: experimental" annotations on new modules

src/data/CCMixmap.mli

@@ -25,6 +25,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 (** {1 Maps with Heterogeneous Values}
 
+{b status: experimental}
+
 @since NEXT_RELEASE *)
 
 type 'a injection

src/data/CCRingBuffer.mli

@@ -23,6 +23,8 @@
     Useful for IO, or as a general-purpose alternative to {!Queue} when
     batch operations are needed.
 
+    {b status: experimental}
+
     @since NEXT_RELEASE
 *)
 

src/lwt/lwt_klist.mli

@@ -30,6 +30,8 @@ Functional streams, that is, lazy lists whose nodes are behind a
 Lwt.t future. Such as list never mutates, it can be safely traversed
 several times, but might eat memory.
 
+{b status: experimental}
+
 @since NEXT_RELEASE *)
 
 type 'a t = [ `Nil | `Cons of 'a * 'a t ] Lwt.t

src/lwt/lwt_pipe.mli

@@ -50,6 +50,8 @@ Lwt_io.with_file ~mode:Lwt_io.output "/tmp/foo"
   );;
 ]}
 
+{b status: experimental}
+
 @since NEXT_RELEASE
 *)