message: add IEnumUnknown
diff: @@ -21,6 +21,17 @@ interface IMalloc(IMallocVtbl): IUnknown(IUnknownVtbl) {
  fn HeapMinimize() -> ()
  }}
  pub type LPMALLOC = *mut IMalloc;
  +RIDL!{#[uuid(0x00000100, 0x0000, 0x0000, 0xC0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46)]
  +interface IEnumUnknown(IEnumUnknownVtbl): IUnknown(IUnknownVtbl) {
  + fn Next(
  + celt: ULONG,
  + rgelt: *mut *mut IUnknown,
  + pceltFetched: *mut ULONG
  + ) -> HRESULT,
  + fn Skip(celt: ULONG) -> HRESULT,
  + fn Reset() -> HRESULT,
  + fn Clone(ppenum: *mut *mut IEnumUnknown) -> HRESULT
  +}}
  STRUCT!{struct STATSTG {
  pwcsName: LPOLESTR,
  type_: DWORD,
  