bug#24386: 24.5; `read--expression' --> `read-expression', please

[Drew Adams]

> > Please consider renaming `read--expression' to `read-expression' and
> > taking away its "internal" designation.  What it does is equally
> > useful to ordinary Emacs user-programmers.
> 
> It does seem like a rather internal function (setting up eldoc stuff
> and the like), so I think it's probably well-named as is; closing.

There's _absolutely nothing_ internal about the
behavior this function offers.  You can use it
_any_ place where you want to read a sexp.

In fact, users should be _encouraged_ to use
this, as opposed to more primitive, less
sexp-oriented ways of reading text when what
they want is a Lisp sexp.

That's akin to telling users to use file-name
manipulation functions instead of just concat,
when dealing with file names.

The name should probably be changed to have
"Lisp" in it, however, as it reads only Lisp
sexps (currently).

And this function needs a doc string (badly).

As for it using `eldoc-mode': That presumably
makes the function more useful for specifically
Lisp-sexp reading.  If we think otherwise then
that could be removed or optional.  In any case,
its presence has _nothing_ whatsoever to do
with whether the function is useful generally
or should be considered internal or local to
only some uses.

This is a bad judgment call, IMHO.