112.06.00

- Made `String_id` have `Stable_containers.Comparable`.
- Changed `Gc.disable_compaction` to require an `allocation_policy`.
- Made `Option` match `Invariant.S1`.
- Added `Sequence.filter`, `compare`, and `sexp_of_t`.
- Added `With_return.with_return_option`, abstracting a common pattern
  of `with_return`.

        val with_return        : ('a return -> 'a  ) -> 'a
        val with_return_option : ('a return -> unit) -> 'a option

- Install a handler for uncaught exceptions, using
  `Printexc.set_uncaught_exception_handler`, new in OCaml 4.02.
- Changed `Day_of_week` representation to a normal variant.
- Changed `Exn.handle_uncaught` so that if it is unable to print, it
  still does `exit 1`.
- Added `Sexp.of_sexp_allow_extra_fields`, previously in
  `Core_extended.Sexp`.
- Changed the implementation of `Exn.raise_without_backtrace` to use
  `raise_notrace`, new in OCaml 4.02.
- Added `Float` functions for converting to and from IEEE
  sign/exponent/mantissa.
- Added `String.Caseless` module, which compares and hashes strings
  ignoring case.
- Reimplemented `Type_equal.Id` using extensible types (new in OCaml
  4.02), removing a use of `Obj.magic`.

    Changed `Type_equal.Id.same_witness` to return `option` rather than
    `Or_error`, which allows it to be implemented without allocation.

- Removed a reference to the `Unix` module. Applications using
  `core_kernel` should be able to link without `unix.cma` again.
- Made `Char.is_whitespace` accept `\f` and `\v` as whitespace,
  matching C.