Parse Pandoc-style citations from Markdown

[hubgit]

1. Add a remark plugin that converts [@foo] to <Cite> markup.
2. Extend the plugin to support prefix, locator, suffix, etc for each citation.

https://pandoc.org/MANUAL.html#citations

https://github.com/jgm/pandoc-citeproc/blob/master/man/pandoc-citeproc.1.md

[hubgit]

https://github.com/benrbray/remark-cite might be useful