Split Command Line and Core Library

[comeara]

Summary

Splits the Pillar command line and core library into separate Maven artifacts.

What's New

• Scala 2.12 support (addresses #39)
• SLF4J default binding (addresses #34)

What's Changed

• Command-line parsing changed to use a subcommand structure
• Command-line parsing carried out by scopt rather than Argot
• ScalaTest upgraded to version 3
• Build refactored to use sbt build definition rather than Scala build definition
• RPM build removed
• Version number set to 3.0.0

[ches]

This looks like a nice step forward, is there anything holding it back?

[comeara]

Only that I had second thoughts about splitting the repo vs keeping related sources in a single repo.