contrib/cfengine-code-style.el: Fix file header and footer lines for ELPA compatibility

This commit makes `cfengine-code-style.el` installable with `package.el`. 

- Fix header line
- Add footer line
- Add Commentary section
- Add Code section
- Change semicolons of header comment lines from three to two

For information about this fix, See following GNU Emacs Manual:
- [Simple-Packages](http://www.gnu.org/software/emacs/manual/html_node/elisp/Simple-Packages.html)
- [Library-Headers](http://www.gnu.org/software/emacs/manual/html_node/elisp/Library-Headers.html)


Re: milkypostman/melpa/pull/1226

/cc @tzz