DIP 1017--Add Bottom Type--Community Review Round 1

[w0rp]

A better name for this type is `never`, which is the name of the 
TypeScript type with similar semantics. 
https://www.typescriptlang.org/docs/handbook/basic-types.html#never `nothing` is also a decent name, used in some other languages, but `never` makes it more obvious that a function never returns, and isn't as easy to confuse with `void`, which is a different kind of nothing.