Publish the Dokka documentation to MavenCentral

MavenCentral makes publishing a JAR containing the documentation of the project mandatory.

Previously, we uploaded an empty JAR. This patch creates a JAR from the Dokkatoo-generated documentation, and publishes that.

This will allow our projects to be visible on sites like https://javadoc.io in the future, allowing users to see old versions of the projects.

Closes #18 (closed)