version 3.0.0-beta2

This Skuber 3 beta release refactors Skuber into three separate modules/libraries with the goal of enabling applications to choose either a Pekko or Akka based client. See the README for details.
This pre-release is based on the 30refactor branch.
The intention is that this pre-release stablizes the dependencies and API for Skuber 3 based applications, but as a pre-release there are no guarantees yet.