Updated docs/emacs

  * emacs.org: enabled 'narrow-to' functions, added comments about
    integration CDLaTeX with AUCTeX, rewrite section about keybinds;
  * (TOP)/emacs.d: auctex-us.el, cdlatex-us.el, keybinds-us.el, emacs:
    updated, tangled from Org document.

Signed-off-by: Vladimir Lomov <lomov.vl@gmail.com>