More Intuitive Syntax for Manifest (enum) Constants

[Walter Bright]

Allow me to point out `static` in C and C++! and its many porpoises!! D takes 
some of that, too. But at least D has `private` instead of `static`.

I agree `enum` for this seems a bit awkward at first, but it smooths out 
naturally pretty quickly. After all, just think of it as an "enumerated 
constant" with only one value, so why bother with the { }.

An enum manifest constant has some subtle differences with `const`:

1. it does not allocate storage

2. it cannot be a pointer

As for `final`, it seems the perfect keyword for it. What semantic integrity is 
it losing? Currently, applying `final` to a variable declaration gives an error.

I have difficulty seeing `macro` being better.