"First edition"

[brucecrevensten]

This PR makes a bunch of changes, but the key theme is the complete integration of all of our content items in a way that could resemble the final draft.

Some code points to see:

• All sections corresponding to our (not-yet-finalized) "top topics" are present on the home page,
• Some "story" type items have been added as an example of the coarse-grained types of Items we can have,
• Tagbar 'works' (for a limited definition of the word 'works').
• Tags are optionally allowed to decorate Items, on an opt-in basis. This looked good to my eye in some places, but in others it was redundant so I decided to make it a choice.
• ⚠️ Tags are now required, and the order matters. The first tag is considered the primary tag associated with the item, which is the one shown if requested.

[brucecrevensten]

Good point on the tags: I made them as subtle as can be without fading away entirely.