[ESS] Polymode is on MELPA

[Stephen Eglen]

> Just use normal buffers and take care that changes from one buffer are
> reflected in all others. Something akin to `linked-buffers` by Phil
> Lord. This might end up in a more fruitfully approach as it would
> potentially allow having different contents in each buffer. You would be
> able to edit roxygen comments in R mode as an example.

Great.

Is there any utility in engaging with Phil and the wider emacs community
to get a good implementation that stands a chance of being adopted more
widely?  I've got time to help with testing, but not much coding time.

Stephen