Enhancement - Hooks

- Implemented API calls: task_get_due, task_get_end, task_get_entry,
  task_get_start, task_get_until and task_get_wait.
- Implemented unit tests for API calls.
- Implemented new Record::get_ulong method.
- Implemented unit tests for get_ulong.

src/Record.h

@@ -47,6 +47,7 @@ public:
   std::vector <Att> all ();
   const std::string get (const std::string&) const;
   int get_int (const std::string&) const;
+  unsigned long get_ulong (const std::string&) const;
   void set (const std::string&, const std::string&);
   void set (const std::string&, int);
   void remove (const std::string&);