core 110.01.00-rc1

# 110.01.00

## async_extra

- Added `Cpu_usage.Sampler` for directly sampling CPU usage.
- Fixed `Log.rotate` to never raise.
- Fixed two bugs in `Log` rotation.
  * Log rotation had used the wrong date when checking whether it
    should rotate.
  * Made `Rotation.keep = \`At_least` delete the oldest, rather than
    the newest, logs.

## async_kernel

- Added `Deferred.Result.map_error`.

## core

- Fixed `Time` unit tests that failed in London because of timezone
  dependence.
- Added `Iobuf.protect_window_and_bounds`, which calls a user function
  and restores the iobuf's bounds afterwards.
- Fixed compilation on OpenBSD, which doesn't support
  `Unix.mcast_join`'s `?source : Inet_addr.t` argument.

## core_kernel

- Changed `Queue` from a linked to an array-backed implementation.

  Renamed the previous implementation to `Linked_queue`.

  Renamed `transfer`, which was constant time, as `blit_transfer`,
  which is linear time.

  Removed `partial_iter`.  One can use `with_return`.

  Added `singleton`, `filter`, `get`, `set`.
- For `Error` and `Info`, changed `to_string_hum` to use `sexp_of_t`
  and `Sexp.to_string_hum`, rather than a custom string format.
- Changed the output format of `Validate.errors` to be a sexp.
- Added `Hashtbl.of_alist_or_error` and `Map.of_alist_or_error`.
- Added `String_id.Make` functor, which includes a module name for
  better error messages.
- Exposed `Bucket.size`.
- Changed the default for `Debug.should_print_backtrace` to be `false`
  rather than `true`.

  Usually the backtraces are noise.
- Removed the tuning of gc parameters built in to Core, so that the
  default is now the stock OCaml settings.

  Such tuning doesn't belong in Core, but rather done per application.
  Also, the Core settings had fallen way out of date, and not kept up
  with changes in the OCaml runtime settings.  We have one example
  (lwt on async) where the Core settings significantly slowed down a
  program.
- Added `Exn.raise_without_backtrace`, to raise without building a
  backtrace.

  `raise_without_backtrace` never builds a backtrace, even when
  `Backtrace.am_recording ()`.
- Made `with_return` faster by using `Exn.raise_without_backtrace`.
- Improved `with_return` to detect usage of a `return` after its
  creating `with_return` has returned.

## ocaml_plugin

- Added `cmi`'s so that plugins can use `lazy`, recursive modules, and
  objects.

## pa_test

- For `<:test_result< >>`, renamed `~expected` to `~expect`

## sexplib

- Added `with sexp` support for mutually recursive types with common
  fields.

  For instance:

  ```ocaml
  type a = { fl : float } and b = { fl : int } with sexp
  ```

  Closes #3
- Fixed the behavior of sexplib on `private` types.

  sexplib used to ignore the `private` modifier, which means generated
  functions had the wrong type.  Now, it generates a function with the
  right type for `sexp_of` and refuses to generate anything for
  `of_sexp`.
- Added `Macro.expand_local_macros`, which macro expands sexps,
  failing on `:include` macros.
- Fixed `Macro`'s handling of nested `:include`'s which was broken
  with respect to paths.

  Prior to this fix, `:include`'s were broken with respect to the path
  used to resolve the filename.  Including a file outside the current
  directory which included another file relative to that one would
  break.