This especially helps braces that surround code blocks.  Back-patch to
v11, where commit 56fb890ace8ac0ca955ae0803c580c2074f876f6 first
appeared; before that, settings were even more distant from perltidy.

Reviewed by Andrew Dunstan.

Discussion: https://postgr.es/m/20190103055355.GB267595@gust.leadboat.com

Now that the documentation sources are in XML rather than SGML, some of
the documentation about the editor, or more specifically Emacs, setup
needs updating.  The updated instructions recommend using nxml-mode,
which works mostly out of the box, with some small tweaks in
emacs.samples and .dir-locals.el.

Also remove some obsolete stuff in .dir-locals.el.  I did, however,
leave the sgml-mode settings in there so that someone using Emacs
without emacs.samples gets those settings when editing a *.sgml file.

Set Emacs's perl-continued-statement-offset to match perltidy's
--continuation-indentation, which is 2 (not overridden in PostgreSQL's
profile) rather than the 4 that Emacs uses by default.

This matches existing practice, but makes the setup complete and
consistent with the C code setup.

Back-patch to 9.4, where .dir-locals.el was introduced.

Update emacs.samples with new configuration snippets that match pgindent
et al. formatting more accurately and follow Emacs Lisp best practices
better.

Add .dir-locals.el with a subset of that configuration for casual
editing and viewing.

Reviewed-by: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
Reviewed-by: Noah Misch <noah@leadboat.com>

Peter Eisentraut

Since both tarballs and git now result in a "postgresql" directory
rather than a "pgsql" directory, adjust the example configuration to
look for the former.

This matches the maximum line length that pgindent uses.