Fix formatting, add autoload cookies

Hi! I'd love to add this to [MELPA](http://melpa.milkbox.net), but the code needs a few little tweaks first, so I thought I'd send you this PR:

- Use standard headers/footers for package.el compatibility
- Add autoload cookies for interactive functions
- Require org at compile time to prevent byte compilation warnings
- Rename `org-in-heading-line` to fit library namespace

Cheers,

-Steve