Expressions Refactor - Clarified expansion rules

- Arg now has a _value member that reflects the value in play, rather
  than the input _raw value.  Only _value is used in eval.
- DOM expansion capabilities are now controlled by rc.dom.

src/E9.h

@@ -73,6 +73,7 @@ private:
   std::vector <Arg> _terms;
   std::map <std::string, RX> _regexes;
   std::string _dateformat;
+  bool _dom;
 };
 
 #endif