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

[Henning Thielemann]

On Mon, 3 Nov 2014, Edward Kmett wrote:

> +1 from me. Storable (Ratio a) probably won't see much use, but it should exist nonetheless to prevent it
> having to be orphaned.

Omitting the Ratio instance it has the advantage that people are warned.