• BC Break: The calendarobjects database table has a bunch of new fields, and a
  migration script is required to ensure everything will keep working. Read the
  wiki for more details.
• BC Break: The ICalendar interface now has a new method: calendarQuery.
• BC Break: In this version a number of classes have been deleted, that have
  been previously deprecated. Namely: - Sabre_DAV_Directory (now:
  Sabre_DAV_Collection) - Sabre_DAV_SimpleDirectory (now:
  Sabre_DAV_SimpleCollection)
• BC Break: Sabre_CalDAV_Schedule_IMip::sendMessage now has an extra argument.
  If you extended this class, you should fix this method. It's only used for
  informational purposes.
• BC Break: The DAV: namespace is no longer converted to urn:DAV. This was a
  workaround for a bug in older PHP versions (pre-5.3).
• Removed: Sabre.includes.php was deprecated, and is now removed.
• Removed: Sabre_CalDAV_Server was deprecated, and is now removed. Please use
  Sabre_DAV_Server and check the examples in the examples/ directory.
• Changed: The Sabre_VObject library now spawned into it's own project! The
  VObject library is still included in the SabreDAV zip package.
• Added: Experimental interfaces to allow implementation of caldav-sharing. Note
  that no implementation is provided yet, just the api hooks.
• Added: Free-busy reporting compliant with the caldav-scheduling standard. This
  allows iCal and other clients to fetch other users' free-busy data.
• Added: Experimental NotificationSupport interface to add caldav notifications.
• Added: VCF Export plugin. If enabled, it can generate an export of an entire
  addressbook.
• Added: Support for PATCH using a SabreDAV format, to live-patch files.
• Added: Support for Prefer: return-minimal and Brief: t headers for PROPFIND
  and PROPPATCH requests.
• Changed: Responsibility for dealing with the calendar-query is now moved from
  the CalDAV plugin to the CalDAV backends. This allows for heavy optimizations.
• Changed: The CalDAV PDO backend is now a lot faster for common calendar
  queries.
• Changed: We are now using the composer autoloader.
• Changed: The CalDAV backend now all implement an interface.
• Changed: Instead of Sabre_DAV_Property, Sabre_DAV_PropertyInterface is now the
  basis of every property class.
• Update: Caching results for principal lookups. This should cut down queries
  and performance for a number of heavy requests.
• Update: ObjectTree caches lookups much more aggresively, which will help
  especially speeding up a bunch of REPORT queries.
• Added: Support for the schedule-calendar-transp property.
• Fixed: Marking both the text/calendar and text/x-vcard as UTF-8 encoded.
• Fixed: Workaround for the SOGO connector, as it doesn't understand receiving
  "text/x-vcard; charset=utf-8" for a contenttype.
• Added: Sabre_DAV_Client now throws more specific exceptions in cases where we
  already has an exception class.
• Added: Sabre_DAV_PartialUpdate. This plugin allows you to use the PATCH method
  to update parts of a file.
• Added: Tons of timezone name mappings for Microsoft Exchange.
• Added: Support for an 'exception' event in the server class.
• Fixed: Uploaded VCards without a UID are now rejected. (thanks Dominik!)
• Fixed: Rejecting calendar objects if they are not in the
  supported-calendar-component list. (thanks Armin!)
• Fixed: Issue 219: serialize() now reorders correctly.
• Fixed: Sabre_DAV_XMLUtil no longer returns empty $dom->childNodes if there is
  whitespace in $dom.
• Fixed: Returning 409 Conflict instead of 500 when an attempt is made to create
  a file as a child of something that's not a collection.
• Fixed: Issue 237: xml-encoding values in SabreDAV error responses.
• Fixed: Returning 403, instead of 501 when an unknown REPORT is requested.
• Fixed: Postfixing slash on {DAV:}owner properties.
• Fixed: Several embarrassing spelling mistakes in docblocks.