Investigate optimal packaging of Scaladoc and Javadoc

[dmanchester]

PlayFOP's Scaladoc and Javadoc are packaged as separate JAR files, with the files named (version number varies):

• playfop_2.12-0.9-SNAPSHOT-scaladoc.jar
• playfop_2.12-0.9-SNAPSHOT-javadoc.jar

There is some precedent for this scheme. Apache Kafka, for example, publishes "scaladoc" and "javadoc" JARs.

It's not clear this scheme is a well-established convention, though. For example, at least in its default configuration, Eclipse and Scala IDE don't seem to know about "scaladoc" JARs:

[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  ::              FAILED DOWNLOADS            ::
[warn]  :: ^ see resolution messages for details  ^ ::
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  :: com.dmanchester#playfop_2.11;0.9-SNAPSHOT!playfop_2.11.jar(doc)

Determine:

• Whether there is a two-JAR convention that's supported by default in major IDEs and build tools.
• If there's a good single-JAR solution. (Maybe sbt-unidoc could be helpful?)