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.
Ok, that's cool.  So, the interface would be the same.  I think the same idea applies: any code related to the local storage version should go into its own module so it can be unit tested.  And the particular native `localStorage` object could be parameterized.