Set Pgx module to wrapped

This makes us only expose the Pgx module at top-level.

Most of this stuff was never intended to be used directly, so the only
major change is that Pgx_value now _must_ be referenced as Pgx.Value.

Fixes #101

pgx/src/dune

@@ -10,7 +10,6 @@ let () = Jbuild_plugin.V1.send @@ {|
 
 (library
  (public_name pgx)
- (wrapped false)
  (libraries hex ipaddr uuidm re sexplib0)
  (preprocess (pps ppx_compare ppx_custom_printf ppx_sexp_conv |} ^ preprocess ^ {|)))
 |}

pgx_value_core/src/pgx_value_core.mli

@@ -1,10 +1,10 @@
 (** Pgx_value types using Core_kernel's Date and Time modules *)
 open Core_kernel
 
-type v = Pgx_value.v [@@deriving compare, sexp_of]
-type t = Pgx_value.t [@@deriving compare, sexp_of]
+type v = Pgx.Value.v [@@deriving compare, sexp_of]
+type t = Pgx.Value.t [@@deriving compare, sexp_of]
 
-include Pgx_value_intf.S with type v := v and type t := t
+include module type of Pgx.Value with type v := v and type t := t
 
 val of_date : Date.t -> t
 val to_date_exn : t -> Date.t