Functor Datatype.Hashtbl.Make

module Make: 
functor (Data : Datatype.S-> Datatype.S with type t = Data.t t
Build a datatype of the hashtbl according to the datatype of values in the hashtbl.
Parameters:
Data : Datatype.S

include Datatype.S_no_copy
val copy : Datatype.t -> Datatype.t
Deep copy: no possible sharing between x and copy x.