Expression reboot

- A3 now tracks whether a command is read-only, and builds filters accordingly.
- Implemented extract_filter, extract_modfications and extract_words stubs.
- Removed all E9 implementation details - this is going to be written from
  scratch.

src/E9.h

@@ -29,44 +29,22 @@
 #define L10N                                           // Localization complete.
 
 #include <string>
-#include <stack>
-#include <Arguments.h>
+#include <A3.h>
 #include <Task.h>
 #include <RX.h>
-#include <Variant.h>
 
 class E9
 {
 public:
-  E9 (Arguments&);
+  E9 (A3&);
   ~E9 ();
-  bool eval (const Task&);
+
   bool evalFilter (const Task&);
-  std::string evalE9 (const Task&);
-  void eval (const Task&, std::vector <Variant>&);
+  std::string evalExpression (const Task&);
 
 private:
-  void expand_sequence ();
-  void implicit_and ();
-  void expand_tag ();
-  void expand_pattern ();
-  void expand_attr ();
-  void expand_attmod ();
-  void expand_word ();
-  void expand_tokens ();
-  void postfix ();
-
-  void tokenize (const std::string&, const std::string&, std::vector <std::string>&, Arguments&);
-  void create_variant (Variant&, const std::string&, const std::string&);
-  bool is_new_style ();
-
-private:
-  bool eval_match (Variant&, Variant&, bool);
-
-private:
-  Arguments _args;
+  A3 _args;
   std::map <std::string, RX> _regexes;
-  bool _prepared;
 };
 
 #endif