Fix library header according to the GNU Emacs Manual

- fix a file header
- add `Package-Requires` header
- change Repository header to URL header
- add `Code` section
- add a footer line

See following URL.
http://www.gnu.org/software/emacs/manual/html_node/elisp/Simple-Packages.html
http://www.gnu.org/software/emacs/manual/html_node/elisp/Library-Headers.html