112.01.00

- Added `Float_ref` module, which is like `float ref` but faster for
  sets due to bypassing the write barrier.

  Benchmark results on Sandy Bridge:

  | [float\_ref.ml:] float ref set  |    2\_886.94ns |   8.00w |            |
  | [float\_ref.ml:] Float\_ref.set |       355.76ns |   6.00w |            |
  | [float\_ref.ml:] float ref get  |       415.52ns |   6.00w |            |
  | [float\_ref.ml:] Float_ref.get  |       416.19ns |   6.00w |            |
- Added `Bin_io_utils.Wrapped.t`, which defines an `'a t with bin_io`
  that supports size-prefixed serialization and deserialization.

  `Wrapped` has two useful submodules, `Opaque` and `Ignored`, for
  efficient handling of size-prefixed bin-io values in cases where
  serialization can be bypassed.  See the comments in the module for
  more details.