Various fixes

- Add autoload cookies for interactive entry point functions
- Fix checkdoc warnings
- Use locate-dominating-file instead of hand-rolled lookalike

That last point is untested, but it should do the trick -- please give it a whirl. :-)

Background: this has arisen from a quick review after receiving your MELPA inclusion request (https://github.com/milkypostman/melpa/pull/935)

-Steve