Docs: remove remnants of static site
Use repo.scala-sbt.org everywhere to be more independent of hosting details.
Docs: add sublit role that processes inline formatting, make default codeliteral role do no additional processing.

This was necessary because too many `` uses had * or | in them.
initial refresh of getting started guide for 0.13: multiple projects and plugins

still todo: Custom-Settings, Full-Def