• Added Sabre\CalDAV\CalendarRoot as an alias for
  Sabre\CalDAV\CalendarRootNode. The latter is going to be deprecated in 2.1,
  so this makes it slightly easier to write code that works in both branches.
• #497: Making sure we're initializing the sync-token field with a value after
  migration.
• The zip release ships with sabre/vobject 3.3.4,
  sabre/http 2.0.4, and sabre/event 1.0.1.