Rules: isolate opinionated trestle Rules support into separate module(s) #1880

Issue description / feature objectives

There is no formal support for rules and checks in OSCAL itself. However, to support automation such support is necessary and trestle has used existing OSCAL features (namely Properties) to embody Rules support. The initial implementation for Rules has been embedded in trestle tasks and core modules. Ideally, the code for Rules support should be gathered into one or a few modules comprising an API that the task and core modules can employ.

• Identify the Rules code throughout the trestle code base
• Create one or more modules to contain the Rules code
• Relocate the Rules implementation code from the task and core modules into the Rule module(s)
• Update the task and core modules to employ the Rules API

Caveats / Assumptions

• Insure all existing test cases continue to pass

Completion Criteria

• Add new test cases to assure 100% coverage for new Rules module(s)