[ESS] shortcut to send a multi-line expression?

[Richard M. Heiberger]

This is a good feature proposal.

We have something very similar in the ess-transcript-mode.

Here, if the point is anywhere on a multi-line statement, then RETURN sends
the whole statement over correctly.  We use the prompts for
information on the location of the beginning and end of the statement.

> abc <-
+   3 *sin(
+    pi)
> abc
>