Make Electric Pair mode smarter/more useful:

Make Electric Pair mode smarter/more useful:

* lisp/electric.el: Pairing/skipping helps preserve
  balance. Autobackspacing behaviour. Opens extra newlines between
  pairs. Skip whitespace before closing delimiters.

* lisp/emacs-lisp/lisp-mode.el (lisp-mode-variables): Use new
  features.

* test/automated/electric-tests.lisp: New file.

* doc/emacs/programs.texi: Describe new features.

* lisp/simple.el: Pass non-nil interactive arg to newline call inside
  newline-and-indent.