Organize dsource by D1/D2?

[dsimcha]

Now that Andrei's book is out and we're declaring D2 ready for prime time,
dsource should be organized such that it's easy to find out what projects are
for which versions of D.  I find it extremely hard to navigate the page when I
need a D2 lib and it's buried in a bunch of D1 libs, and I imagine newcomers
who don't even know about the fact that there are two different versions will
feel even more that way.