Update Emacs configuration

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>