Hello Ghosts and Ghouls,

After a period of spooky deliberation and well-received release candidate, Koz and I are pleased to announce `mtl-2.3.1`, which features the following hellish changelog:

* Add `modifyError` to `Control.Monad.Error.Class`, and re-export from

  `Control.Monad.Except`.

* Make the `MonadCont` instance for `ContT` more polykinded; now, `r` is allowed

  to be of an arbitrary kind `k`, rather than only `Type`.

* Add a generic `liftCallCC` for use with any `MonadTrans`.

* Add `modifyError` to `Control.Monad.Error.Class`

* Return re-export of `ExceptT` and related functions to `Control.Monad.Except`.

* Add `label` function to `MonadCont`

If you wish to migrate to `mtl-2.3.x` and have not yet done so, please refer the migration guide in the repo: https://github.com/haskell/mtl/blob/master/docs/Mtl-2.3.x-Migration.md

A release has been published on the github repository under the tag v2.3.1.

Happy Halloween!

Emily + Koz