Preprocessor scope/tree parser.

[webbju]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

• Add pre-processor directive parser which identifies the "scopes" of conditional logic.
  • Scopes are contextual to the script/document; so they track line/column and indexes of start and end positions.

[nemui]

lgtm