1. Added following constant MAP_GAP_IN_DAYS_BETWEEN_MONDAY_AND_OTHER_WEEKDAYS in module CalendarConstants.

2. Added following class method in class Calendar
		date_on_first_monday_of_year
   Added the specs for the same.

3. The Calendar.week_number_of_year(time=Time.now) class method's previous
   implementation was buggy. It was not returning correct week-number of
   year for the given date. Fixed it and added more examples to the specs
   testing the implementation correctness.