Consider importing server, JSON config utilities from mbland/custom-links

Per mbland/custom-links#138, functions from [`scripts/serve`](https://github.com/mbland/custom-links/blob/e1e6a656ca4e64842200472e964f9054e1df8115/scripts/serve) and [`scripts/lib/config-json`](https://github.com/mbland/custom-links/blob/e1e6a656ca4e64842200472e964f9054e1df8115/scripts/lib/config-json) may prove useful to import into `lib`.