Add NonEmptyMap and NonEmptySet to containers

[Henning Thielemann]

On Fri, 19 Apr 2019, chessai . wrote:

> I'm also +1.
> Why not:
> 
> Data.Map.NonEmpty
> Data.Map.NonEmpty.Lazy
> Data.Map.NonEmpty.Strict
> 
> If sets are added as well:
> 
> Data.Set.NonEmpty

+1 for these module names.