add Storable a => Storable (Ratio a) and Storable a => Storable (Complex a) to base

[Herbert Valerio Riedel]

On 2014-11-03 at 17:07:25 +0100, Carter Schonwald wrote:
> Getting those two into base for 7.10 would be quite nice.
>
> I think this will mostly impact folks who maintain numerical computing
> libraries, such as myself, and even then, I think this would be a change
> well worth having!
>
> discussion period 1 week  (because I'd like to get it OK'd with plenty of
> time before the merge window for 7.10 finally closes)

I'm +1 for the `Storable (Complex a)` instance; 

I am, however, +0.1 for `Storable (Ratio a)`

(I'm not for it as it doesn't seem too useful (and hence used) for
bounded types such as fixed-width integer, otoh I'm not totally against
an instance it as it'd help avoid the temptation of orphan instances as
pointed out in the discussion so far)