111.28.00

- Added `Pooled_hashtbl.resize` function, to allow preallocating a table
  of the desired size, to avoid growth at an undesirable time.
- Added `Pooled_hashtbl.on_grow` callback, to get information about
  hashtbl growth.
- Changed `Hashable.Make` to not export a `Hashable` module.

    The `Hashable` module previously exported was useless, and shadowed
    `Core.Std.Hashable`.

- Moved `Common.does_raise` to `Exn.does_raise`, to make it easier to
  find.
- Added `Float.one`, `minus_one`, and `~-`.  (fixes #12).
- Removed `Core.Std.unimplemented` and renamed it as
  `Or_error.unimplemented`.

    It is not used enough to live in the global namespace.