Expressions

- Improved strictness of attr and attmod detection, although it needs
  more.
- Added unit tests arguments.t.cpp, to test the detection methods.

src/Arguments.h

@@ -51,6 +51,7 @@ public:
   void resolve_aliases ();
 
   std::vector <std::string> list ();
+  static std::vector <std::string> operator_list ();
   std::string combine ();
 
   bool find_command (std::string&);