Enable scaladoc and "classical" comments

It turns out that `/**` comments fail with the `-Xlint` option, so I just removed it for the `doc` task.
Also there is a weird literal inference with Scaladoc and the `Date` macro. My fix doesn't seem to affect the production code, just the Scaladoc production.
My sbt isn't good enough to decipher this. I assume it just translates to exactly what we have now for everything except doc.