Bake in citations at build time

Nobody has claimed this yet.

The `citation` include accepts a `doi` (or `id`, which then retrieves a DOI), bakes that into as a simple metadata-laden `span` that gets be rewritten by JavaScript upon page load, via the excellent citation-js library. However, we can do better: we could do the DOI resolution with a Jekyll plugin at build time, so the citations get baked into the static HTML during site build, rather than re-resolved on every page load on every person's computer.

The [jekyll-scholar](https://github.com/inukshuk/jekyll-scholar) plugin could be a good starting point, although I don't think it does what we need yet... but would be generally awesome to augment it to use citation-js to fill in the `.bib` data internally and then go from there?

Start by reviewing the existing citation include and how citation-js currently resolves DOI or id values in the generated site. Then compare jekyll-scholar's build-time behavior and assess how it could use citation-js to fill .bib data internally. Done means citations are resolved during the Jekyll build and emitted as static HTML without page-load resolution.

Written by the indexing model from the issue text.