Updated emacs

  * emacs.d/auctex-us.el: added comments about cdlatex minor mode and
    code to make it works if only one, LaTeX document is edited in
    Emacs.
    Explanation: previously CDLaTeX mode works because LaTeX document
    was open in Emacs in parallel with Org document which in turn uses
    CDLaTeX minor mode so AUCTeX "knows" about the MM. But if only one,
    LaTeX document is open then CDLaTeX MM is not on because AUCTeX
    doesn't know where symbols (functions) are defined.

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