added alias 'flatten' for 'concat'

sequence.ml

@@ -109,6 +109,8 @@ let concat s =
     let k_seq seq = iter k seq in
     s k_seq)
 
+let flatten s = concat s
+
 (** Monadic bind. It applies the function to every element of the
     initial sequence, and calls [concat]. *)
 let flatMap f seq =

sequence.mli

@@ -101,6 +101,9 @@ val append : 'a t -> 'a t -> 'a t
 val concat : 'a t t -> 'a t
   (** Concatenate a sequence of sequences into one sequence *)
 
+val flatten : 'a t t -> 'a t
+  (** Alias for {!concat} *)
+
 val flatMap : ('a -> 'b t) -> 'a t -> 'b t
   (** Monadic bind. It applies the function to every element of the
       initial sequence, and calls [concat]. *)