Code Cleanup

- Remove the code related to the format "day of year" (number of day starting
  from the January 1) as mktime does not allow to specify it with the field
  tm_yday.
- Cleaner check of the date (everything is done by Date::valid).
- Correct hour, minute and second is also checked.

src/Date.h

@@ -67,6 +67,7 @@ public:
   static time_t easter (int year);
   static bool leapYear (int);
   static int daysInMonth (int, int);
+  static int daysInYear (int);
   static std::string monthName (int);
   static void dayName (int, std::string&);
   static std::string dayName (int);