Improve the ergonomics of core.atomic

[IGotD-]

On Thursday, 1 October 2020 at 14:35:01 UTC, Jackel wrote:
>
> One reason could be that it is much more obvious what 
> operations are atomic when reading. The syntax isn't as nice, 
> but you know the operation is atomic.

The current atomic template functions don't need to be removed 
and they can be used if the programmer wish to use them just as 
before. A new atomic template type would just be an addition that 
doesn't break old code.