First cut at referencing one property from another.
Changes after review.
Update Java
Fix empty doc.
Refactor PositionList to write out an array of reference objects instead of strings.
Ongoing reference work

Write out a single reference string instead of separate id and path.  Add helper overloads to enable automatic escaping when needed.  Still need documentation, tests, and actual value escaping.
Ongoing reference work.
Ongoing cleanup.
Update Java
Doc cleanup.
Make sure a Reference writer is generated

Factor out ReferenceValue.jsonschema from Reference.jsonschema to be consistent with all of the other properties and writers.
Ongoing reference work.
Delete unused file.
Only leaf properties can currently be references.
Some additional cleanup.
I forgot to update Java.
Changes after review.
Java fixes.
Fix remaining Java failures
Merge pull request #66 from AnalyticalGraphicsInc/reference

Reference properties