Support Calendar extensions

vCalendar and iCalendar support private software extensions, with a X- prefix, a number of which are in common usage these days. This release bring in the next X- prefix variables into iCalendarkit.

• X-MICROSOFT-CDO-ALLDAYEVENT in ICalendarEvent
• X-MICROSOFT-CDO-BUSYSTATUS in ICalendarEvent
• X-MICROSOFT-CDO-INTENDEDSTATUS in ICalendarEvent
• X-MICROSOFT-CDO-IMPORTANCE in ICalendarEvent
• X-WR-CALNAME in ICalendar
• X-WR-CALDESC in ICalendar
• X-WR-RELCALID in ICalendar
• X-PUBLISHED-TTL in ICalendar

Time Zone Component Added.

This version introduces the Time Zone Component into iCalendarKit.

Tag for current version.

Merge pull request #11 from swift-calendar/date-hotfix

ICalendarDate Hotfix