Honor existing :refer :all requires

From #29

> The ability to add :refer :all namespaces on a per-project basis might
> be good

I think that's a great solution.

> but I haven't figured out a clean way to pass configuration options to
> slamhound

A no-configuration way is to simply honor existing :refer :all imports
and move on (but not :use!). When the user decides he'd like to tidy his
namespace, he can simply remove that expression and re-run Slamhound.

https://github.com/technomancy/slamhound/issues/29#issuecomment-22086914