draft proposal for Sum Types for D

[Adam D Ruppe]

On Wednesday, 30 November 2022 at 03:23:42 UTC, Walter Bright 
wrote:
> As I expected, the threads on sum types have a lot of posts, 
> and each reply I make spawns many more. I apologize if I don't 
> respond in depth to all of them.

This phenomenon is what prompted my newest blog post:
http://dpldocs.info/this-week-in-d/Blog.Posted_2022_11_28.html#dip-dip,-part-2

I'd formalize some of the feedback stuff to ensure discussions 
happen before feedback and to remove duplicates.