Wingtips enabled presentations

Introduces the `wingtips` gem and shuffles things around for the existing presentations

`bin/wingtips` is here just as a helper for running from source.

A `wingtips` presentation expects this layout:

```
presentation_folder/
  config.rb
  slides/*.rb
  code/*.rb
  images/*.*
```

You can run it by doing `bin/wingtips presentation_folder` (will default to looking up `config.rb` if given just the folder name)

I made some individual tweaks here and there in the code that got lost when I moved the files since I'd set a separate repo when I was working... hopefully no big surprises there.

FWIW, the one problem I've noticed running with the actual shoes gem is that we don't include `lib/ext/**/*` in any of the gems, and that's the code highlighting that we're using here in `wingtips`

Happy to address anything you see here, but I probably should get down to actually writing my presentation :sweat_smile: