Expressions

- Reordered operator table so that longer operators match first, thus
  disambiguating between ! and !=.
- Eliminated Expression::expand_expression.
- Modified Nibbler to know what a DOM reference looks like.
- Removed alpha equivalent operators (lt, le, gt, ge, not, eq, ne) because
  these are common in descriptions (French: le, ne).
- Modified Arguments and Nibbler unit tests.

src/Nibbler.h

@@ -65,6 +65,7 @@ public:
   bool getDateISO (time_t&);
   bool getDate (const std::string&, time_t&);
   bool getOneOf (const std::vector <std::string>&, std::string&);
+  bool getDOM (std::string&);
 
   bool skipN (const int quantity = 1);
   bool skip (char);