[phobos] New time lib

[Steve Schveighoffer]

I think Phobos should include this, it looks very well written:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.announce&article_id=18075

It's very similar to the improvements I made to Tango a while back, but with well thought-out improvements to the interface to get it D2 shape.

My preference would be to put the Span part into druntime, and the rest into a phobos module.  This allows things like Thread.sleep to use Span.

-Steve