Updated change tracking in the ELM expression schema.
Updated change tracking in the ELM expression schema.

MeasureAuthoringTool/clinical_quality_language,DBCG/cql_engine,DBCG/cql_engine,cqframework/clinical_quality_language,MeasureAuthoringTool/clinical_quality_language,wanghaisheng/clinical_quality_language-Research,MeasureAuthoringTool/clinical_quality_language,cqframework/clinical_quality_language,wanghaisheng/clinical_quality_language-Research,wanghaisheng/clinical_quality_language-Research,MeasureAuthoringTool/clinical_quality_language