The initial spec was a bit optimistic about how much would be
accomplished in Xena. Additionally, this initiative has been
formalized as a multi-cycle community goal and the direction of
the effort has been revised and expanded. So update the Xena
spec to reflect what was actually done in Xena, and add a new
spec for the continuation of this work in Yoga.
Change-Id: If6c289d6957bd739ed893f01519441e6039a7d00
de4308f4a7