bug#50929: Add slurp-sexp and barf-sexp

[Philip Kaludercic]

Richard Stallman <rms@gnu.org> writes:

> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> [[[ whether defending the US Constitution against all enemies,     ]]]
> [[[ foreign or domestic, requires you to follow Snowden's example. ]]]
>
> What does slurp-sexp do?
> What does barf-sexp do?

Given two expressions like

(save-excursion
  |(foo))
(bar)

where "|" is the position of the point, slurp-sexp would transform this
into

(save-excursion
  |(foo)
  (bar))

and barf-sexp would reverse this change. 

> If we want to have those operations, let's find less gross names for
> them.

I reused the names that other structural editing packages use, but they
could be renamed into somthing like pull-sexp/ and push-sexp just as
well.

-- 
        Philip Kaludercic