message: Update the changelog re: Clone and .copy()
diff: - Added basic support for reading and writing dataset slices.
  - When creating datasets, in-memory type layouts are normalized (converted to C repr).
  - Added `packed` option to `DatasetBuilder` (for creating packed HDF5 datasets).
  +- All high-level objects now implement `Clone` (shallow copy, increases refcount).
  ### Changed
  user can user methods of the parent type without having to import any traits into scope
  (for instance, `File` dereferences into `Group`, which dereferences into `Location`,
  which dereferences into `Object`).
  +- Dataspaces and property lists can now be copied via `.copy()` method (instead of `.clone()`).
  ### Fixed
  