As it often happens, release a new version and almost immediately realize that it could have been easily improved on.

I've just updated Pinboard Poster to version 0.9.3, adding more ways to initialize:

val poster = PinboardPoster(Paths.get("local.properties")) // uses default PINBOARD_API_TOKEN key
val poster2 = PinboardPoster(Paths.get("my.properties"), "my.api.key")
val p = Properties()
p.setProperty("api.key", "user:TOKEN")
val poster3 = PinboardPoster(p, "api.key")

As usual documentation and source are on GitHub.