(R)Stan 2.0 schedule

[Bob Carpenter]

EXEC SUMMARY:

* Stan 2.0 beta testing in approximately two weeks.
* Official Stan 2.0 version in approximately a month.
* RStan 2.0 on roughly the same schedule

Longer version:

We froze features at our meeting early last week.

The triage on features left out of Stan 2.0 can be seen on
the issue tracker on GitHub by inspecting the milestones.

Late last week, Daniel and Michael managed to clear the
hurdle of integration testing for the new argument structure,
which is much more flexible and coherent and extensible than
what we had before.

All that's left to do now is

* integrate the pileup of pull requests,
* fix a couple (hopefully minor) bugs, and
* update the docs with all the great comments we've gotten
(keep them coming --- we do track them and pay attention)

We still have to coordinate with Jiqiang about RStan, and
my understanding is that the interfaces there won't change
as much as for Stan. We've decoupled the projects' repositories,
and there's no reason for them to be completely synchronized
other than not to disappoint our R users (which is probably
most of our users at this point --- it's certainly how I use
Stan most of the time).

The next message on this topic will hopefully be beta-test
announcements (of course it'll be open --- everything in Stan's
open).

- Bob