Made easter algorithm static in Date

src/Date.h

@@ -30,7 +30,6 @@
 #include <stdio.h>
 #include <string>
 
-time_t easter (int year);
 
 class Date;
 
@@ -55,6 +54,7 @@ public:
   static bool valid (const int, const int, const int, const int, const int, const int);
   static bool valid (const int, const int, const int);
 
+  static time_t easter (int year);
   static bool leapYear (int);
   static int daysInMonth (int, int);
   static std::string monthName (int);