use proper section headings to separate packages

Instead of e.g.

   ;; package

use

;;;;; package

This allows collapsing sections similar to how this is done in Org
mode.  The outshine minor-mode can be used to achieve them same in
Emacs-Lisp and other major-modes.
mention rainbow-mode above color palette
remove semicolon-only lines around commentary
remove empty line at end of package sections
Merge pull request #105 from tarsius/master

For easier navigation and hiding: use proper section headings to separate packages