Support of every n days, every n months and every n years
New way to find date range for next and previous occurrences as it was giving wrong values for some events.
Added unit tests for month and year. Updated unit tests for DailyTests.
Added missing reference for YearTests.cs
Refactored method 'DateRange'.
additional refactoring of daterange method
Merge pull request #10 from jerryjoseph/EveryNDaysMonthsYearsSupport

Every n days months years support