Add publish doc tasks

[wsargent]

sbt-release-early only publishes documentation on tag, and updating the doc website from a branch means the version number is screwy. Fix it so updating docs from a branch shows the last tagged version.

Might also be a good idea to namespace the docs by version number so we can refer back to earlier docs.

can use old version

lazy val oldVersion = "git describe --abbrev=0".!!.trim.replaceAll("^v", "")

https://github.com/plokhotnyuk/fast-string-interpolator/blob/master/build.sbt#L4