Reorganize Org exporting settings.
Set org-latex-default-class.
Set org-beamer-frame-level.
Replace ruby-mark-defun with mark-defun.

ruby-mark-defun has been obsolete since Emacs 24.3, and replaced with
mark-defun.
Install Rsense.
Add a new electric pair, ||, to ruby-mode.
Merge branch 'ruby-mode-improvement'