Publish API docs

[travisbrown]

We have sbt-unidoc set up and I've been using it locally, and we could pretty easily publish the API docs now with sbt-ghpages, but the Scaladoc presentation of the Java API docs is pretty terrible in my view, and I'd rather wait and take the time to do this more nicely (probably by publishing the Javadoc and Scaladoc sites separately—I think I'd give up cross-Java-Scala-module linking to have real Javadoc output for the Java modules).