…#143)

* Make the current artifact configurable.

This enhances the flexibility of the plugin.

* Change the default for `mimaCurrentArtifact` to `jar`

This is to also take all potential post processing (filtering, shading, OSGi bundling) into account.
This is IMHO a better default than `compile().classes`, but if someone needs the old behavior, it's now configurable.

* doc

* ScalaDoc

* scalafmt