Implement a Control.Exception.Checked.{Lifted,Unlift} module

[shajra]

I'm kind of eager to use Checked with monad transformers, and not just a raw IO.

monad-control doesn't have a great user experience (the boilerplate to create MonadBaseControl and MonadTransControl instances, for example), but it does solve a problem with monad transformers; we want to be able to unstack the transformer stack to get to the base, run a function, and then stack everything back again.

And as a second step, maybe make another module for unliftio. That way I'm not forcing people to chose between MonadBase and MonadIO.

But maybe this is all a low priority because the exceptions approach of Monad{Catch,Throw,Mask} can go far enough.