Make headers conform to package.el requirements

We'd like to add a [scion package](https://github.com/milkypostman/melpa/pull/585) to [MELPA](http://melpa.milkbox.net/), but the headers (and footer line) are not `package.el`-compliant, so an installable package cannot be built.

This commit reformats the header slightly, and adds the required trailing "ends here" line.