Scaladocs should link directly to the page, not to the index

[jroper]

Currently, Paradox only links directly to the page if the Scala version is 2.12. But Scaladocs (since at least Scala 2.10) will redirect you to the framed version automatically when you visit the page directly. Linking directly to the page helps SEO, is friendly to crawlers, and also works when javascript is disabled. There's no good reason to link to the index file with the class in the fragment that I can see.