Prepare for CDM Integration

[dschwartznyc]

This release adds support for metadata and for serialization / deserialization consistent with the serialization specifications in CDM issue #3236. It closes PR 26

Also included is support for:

• circular Type definitions
• increased testing of operators
• generating Python across multiple namespaces
• Command line (CLI) generation of Python from a Rune source file or directory. To execute the CLI (assuming
  the default process wherein the JAR is built in the target directory):

 java -cp target/python-0.0.0.main-SNAPSHOT.jar com.regnosys.rosetta.generator.python.PythonCodeGeneratorCLI -s [rune source files] -t [target directory for generated Python]

The CLI will be used by CDM to generate Python.

This release also includes an action to generate a PR when the Rune DSL version changes.