Organizing 3.0

[JacquesCarette]

@jamesmckinna mentions that we ought to have a shopping list issue for 3.0.

I think that using issues for that is sub-optimal. I'd prefer to either use the Wiki or turn on 'Discussions' for agda-stdlib have have the discussion there. I'm open to other ways too - but I find very long issue threads to be a nightmare to sort out. To me, optimal would be:

1. various Discussion threads for 3.0-related ideas
2. page(s) on the wiki to organize the conclusions