Rename D newsgroup to D.core

[John J]

A small suggestion:
Renaming the current D newsgroup to D.core will make the new comers to 
look for other available groups and find the D.learn

Otherwise, they either post to D group asking beginners questions or 
they simply watch the most complex and intimidating core language 
discussions in this group and runaway thinking the language is still 
being designed and not ready yet.