Code Cleanup

- Migrated the recur.cpp getDueState() function into Task::getDateState(),
  which can assess any date attribute.
- Improved implementation to distinguish between:
    - not due, or not due for rc.due days
    - due after today
    - due later today
    - due earlier today
    - due before today
  This greater precision should address some outstanding issues.

src/Task.h

@@ -72,6 +72,9 @@ public:
   // Status values.
   enum status {pending, completed, deleted, recurring, waiting};
 
+  // Date state values.
+  enum dateState {dateNotDue, dateAfterToday, dateLaterToday, dateEarlierToday, dateBeforeToday};
+
   // Public data.
   int id;
   float urgency_value;
@@ -117,6 +120,8 @@ public:
   status getStatus () const;
   void setStatus (status);
 
+  dateState getDateState (const std::string&) const;
+
   int getTagCount () const;
   bool hasTag (const std::string&) const;
   void addTag (const std::string&);