Add feature to show/hide bits of a guide based on preferences

Add support for embedded CSS classes that allow hiding segments of a guide based on build systems. Embed these selections in a cookie so that preferences are carried across various guides.
This cookie management object is a great candidate to move to its own module, so that it's visible for unit testing.  Switching it to a constructor + prototype, and parameterizing the constructor with a `document` would make for even easier unit testing: you could pass in a fake/mock document for testing.