API C Calendar.OpenEvent

Establishes an event for future calendar API calls
 success = C_Calendar.OpenEvent(offsetMonths, monthDay, index)
==Arguments==
:;offsetMonths: - The number of months to offset from today.
:;monthDay: - The day of the month on which the desired event is scheduled (1 - 31).
:;index: - Ranging from 1 through (offsetMonths, monthDay).
==Returns==
:;success:
==Patch changes==