Set scroll-margin in custom-variables
Switch from autopair to smartparens

The smartparens package also negates the need for ruby-electric-mode,
and doesn't play nice with cua-mode. But my use of cua-mode was due to a
bug between ECB and delete-selection-mode, which seems to now be
fixed. Hence cua-mode is out too.
Reorganize keybindings.el file a bit
Improve multiple-cursors keybindings