[Emacs] Various fixes

Saw this on reddit, and I'd like to add it to [MELPA](http://melpa.milkbox.net/) so that your users can trivially install it in recent emacsen.

Along the way, I had a quick look through the source and thought I'd contribute a few improvements.

- Full header boilerplate
- Autoload major mode and auto-mode-alist
- Use define-derived-mode instead of hand-rolled mode function
- Inherit faces from standard outline-* faces by default, so that themes will influence the colors
- Fix (almost all) byte compilation warnings
- Fix some docstrings

Now, these are untested, so please double-check them.

Still desirable would be to add a little info in the `Commentary` section of the file, and to run `M-x checkdoc` to clean up the docstrings.