Small fixes in doc

src/ocsipersist.mli

@@ -1,5 +1,5 @@
 (** Persistent key-value store interface for OCaml.
-    This is an virtual library defining a unified frontend for a number of
+    This is a virtual library defining a unified frontend for a number of
     key-value storage implementations. Implementations of the following backends
     currently exist: SQLite, DBM, PostgreSQL.
     You can choose the backend you prefer by installing packages

src/ocsipersist_lib.ml

@@ -160,12 +160,12 @@ module Sigs = struct
     val ref : ?persistent:string -> 'a -> 'a t
     (** [ref ?persistent default] creates a reference.
         If optional parameter [?persistent] is absent,
-+       the reference will not be persistent (implemented using OCaml references).
-+       Otherwise, the value of [persistent] will be used as key for the
-   +    value in the persistent reference table.
+        the reference will not be persistent (implemented using OCaml references).
+        Otherwise, the value of [persistent] will be used as key for the
+        value in the persistent reference table.
         If the reference already exists, the current value is kept.
-+       Be careful to change this name every time you change the type of the
-+       value. *)
+        Be careful to change this name every time you change the type of the
+        value. *)
 
     val get : 'a t -> 'a Lwt.t
     (** Get the value of a reference *)