[OCaml] Add Token type to kind enum in OCaml API

[jberdine]

Summary

The token type has not yet been added to the OCaml API. This
patch only extends the enum, so that e.g. classify_type will not
crash. No support for manipulating or building tokens is added at this
point.

[whitequark]

LGTM

bindings/ocaml/llvm/llvm.ml

module TypeKind = struct
   | Integer
   | Function
   | Struct
   | Array
   | Pointer
   | Vector
   | Metadata
   | X86_mmx
+  | Token
 end
 
 module Linkage = struct
   type t =
   | External
   | Available_externally
   | Link_once
   | Link_once_odr

bindings/ocaml/llvm/llvm.mli

module TypeKind : sig
   | Integer
   | Function
   | Struct
   | Array
   | Pointer
   | Vector
   | Metadata
   | X86_mmx
+  | Token
 end
 
 (** The linkage of a global value, accessed with {!linkage} and
     {!set_linkage}. See [llvm::GlobalValue::LinkageTypes]. *)
 module Linkage : sig
   type t =
     External
   | Available_externally