Log Message:
Update to 4.0

CHANGELOG:
4.0
 * Added `nearly` to `Control.Lens.Prism`.
 * Added `Control.Lens.Empty`, exporting `_Empty`.
 * We now require `DefaultSignatures`.
 * Added `failing` and `ifailing` to `Control.Lens.Traversal`.
 * Changed the signature of `Data.List.Split.Lens.condensing` due to the
   addition of `DropBlankFields` to `Data.List.Split.CondensePolicy` in
   `split`.
 * Simplified `Each`, `Ixed`, and `Contains`. They are no longer indexed.
   The previous design was actively getting in the way of user-defined
   instances.
 * Replaced more of our home-grown types with standard ones. They had
   previously been defined to help make more intelligible error messages, but
   when we switched to using `(Contravariant f, Functor f)` instead of
   `(Gettable f)`, these no ceased to really help. Now you can define even
   more `lens`-compatible types (e.g. `Getter` and `Fold`) without depending
   on `lens`.
 * Replaced the use of `Accessor` with `Const`.
 * Replaced the use of `Mutator` with `Identity`.
 * Replaced the use of `Reviewed` with `Tagged`.
 * Removed the deprecated `Control.Lens.Simple` module.
 * Repurposed `Control.Lens.Combinators` to reﾃｫxport `Control.Lens`
   sans any operators; previous residents rehomed to `Control.Lens.Lens`.
 * Added `Control.Lens.Operators` to export just the operators. Varying
   your import styles between these supports many qualified usage scenarios.
 * Simplified `Cons` and `Snoc`. Now they must be a `Prism`.
 * Simplified `Contains`. This necessitated losing many instancs of
   `Contains`, but makes it much easier and more consistent to use and
   instantiate.
 * Simplified the various `AsFoo` types in `Control.Exception.Lens`
 * Simplified the types in `System.IO.Error.Lens`.
 * Merged `lens-aeson` into `lens`.
 * We're exiling `Control.Lens.Zipper` to a separate package. This will let
   the design for it iterate faster and let us explore the trade-offs between
   the 3.8 style and the 3.9 style of zippers.
 * Generalized `alongside`, `inside`, `both`.
 * Switched to a new `Typeable` version of `reflection` for the harder
   combinators in `Control.Exception.Lens`. This enables us to comply with
   GHC 7.7's ban on hand-written `Typeable` instances.
 * Added a `_Show` `Prism`.
 * Added `Control.Lens.Extras` for the combinator names we don't have the
   gall to claim outright, but which are consistent with the rest.
 * Renamed the constructors for `ReifiedLens`, etc. to just be the name of
   their base type.
 * Added many many missing instances for `ReifiedFold` and `ReifiedGetter`.
   This permits things like `runFold ((,) <$> Fold (traverse._1) <*> Fold
   (traverse._2))` to be a `Fold`
   and `ReifiedFold` can be used as a `Monad`, `Profunctor`, etc.
 * Many performance optimizations.
 * Switched to `exceptions` from `MonadCatchIO-transformers`
 * Added types for working with `RelevantFold` and `RelevantTraversal`.
   These are a `Fold` or `Traversal` that always has at least one target.
   Since `Apply` isn't a superclass of `Applicative`, you occasionally need
   to convert between them, but it lets you more readily work with less
   unsafety.
 * Changed `unwrapping` and `wrapping` to have the same
   constructor-oriented order as a `Prism` and renamed them t `_Wrapping` and
   `_Unwrapping` respectively. 
 * Drastically changed the way `_Wrapping` and `_Unwrapping` are built to
   get much better inference.
 * There are about 15,000 lines of patches over the last year, so I'm sure
   we missed a few big changes.