Add static search sub-app

[srid]

https://ema.srid.ca/guide/compose

Much like Ema.Route.Lib.Extra.PandocRoute, we want an Ema.Route.Lib.Extra.StaticSearch that uses https://stork-search.net/ to provide client-side full-text search to static sites.

Ultimately this should be used in Emanote: srid/emanote#327 | https://emanote.srid.ca/guide/html-template/search

[srid]

All sub apps must be a separate package; see #141