This is a convenience module in order to have less import noise. It
re-exports the following:
a) Commonly used modules in full (Data.Foldable, Data.Applicative, and
so on); though only those that play nicely with each other, so that
XMonad.Prelude can be imported unqualified without any problems.
This prevents things like `Prelude.(.)` and `Control.Category.(.)`
fighting with each other.
b) Helper functions that don't necessarily fit in any other module;
e.g., the often used abbreviation `fi = fromIntegral`.
Drop Eq constraint that isn't needed.
Drop the redundant Maybe from findZ return type. Breaks symmetry but
makes it easier to use (join no longer needed).
* Explicitly import pure, (<$>), (<*>) and (<$) from Control.Applicative.
* Use DeriveDataTypeable pragma.
* Remove type signature from pattern synonym.
