Void type in base

[David Luposchainsky]

Hey Libraries,

a couple of weeks ago Shachaf proposed adding Void to Base ("Void type
in base", 2013-07-17). The discussion period of 2 weeks is over, and
there does not seem to be any further discussion of the topic.

I think the responses were generally in favour of `Void` and `absurd`,
with somewhat mixed opinions on naming and `vacuous`.

Maybe we should take the time to finish this proposal up? A reminder,

> The proposal is just to copy the Data.Void API into base:
>
>     data Void -- EmptyDataDecls is in Haskell 2010
>     absurd :: Void -> a
>     vacuous :: Functor f => f Void -> f a
>     -- instances for Typeable, Data, Generic, Eq, Ord, Show, Read,
>     -- Ix, Exception

I'm not sure about vacuous, it was mentioned that it's only historical
(also it's just `fmap absurd` so easily reproducable), which means it
would be adding something almost deprecated or redundant to Base (old
packages could still import the current void package to get that
function if necessary).

Anyway, +1 in general, independent of the previous remark.

David