111.17.00

- In `Bigstring`, made many operations use compiler primitives new in
  OCaml 4.01.

  Exposed `Bigstring.get` and `set` as compiler primitives in the
  interface.

  Added `Bigstring.unsafe_get_int64_{le,be}_trunc`.
- Made `Error` round trip `exn`, i.e. `Error.to_exn (Error.of_exn exn)
  = exn`.
- Added to `failwiths` an optional `?here:Lexing.position` argument.
- Added `with typerep` to `Flags.S`.
- Optimized `List.dedup []` to return immediately.
- Added `data` argument to polymorphic type `Hashtbl_intf.Creators.create_options`.

  This allows implementations of `Hashtbl_intf.Creators` to have
  constructor arguments that depend on the type of both key and data
  values.  For example:

  ```ocaml
  module type Hashtbl_creators_with_typerep =
    Hashtbl_intf.Creators
    with type ('key, 'data, 'z) create_options
      =  typerep_of_key:'key Typerep.t
      -> typerep_of_data:'data Typerep.t
      -> 'z
  ```
- Improved the interface for getting `Monad.Make` to define `map` in
  terms of `bind`.

  Instead of passing a `map` function and requiring everyone who wants
  to define `map` using `bind` to call a special function, we use a
  variant type to allow the user to say what they want:

  ```ocaml
  val map : [ `Define_using_bind
            | `Custom of ('a t -> f:('a -> 'b) -> 'b t)
            ]
  ```
- Improved the performance of many `Dequeue` functions.

  Previously, many `Dequeue.dequeue`-type functions worked by raising
  and then catching an exception when the dequeue is empty.  This is
  much slower than just testing for emptiness, which is what the code
  now does.

  This improves the performance of `Async.Writer`, which uses
  `Dequeue.dequeue_front`.