Upstream changes#2

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RobToMars wants to merge 23 commits intoRobToMars:masterfrom

Commits on Jan 18, 2018

Add startTZID and endTZID fields to events
zerok
committed

Commits on Feb 23, 2018

Add support for DURATION value
ppikula
committed

Commits on Aug 2, 2018

Manage language prefixed summaries in accordance with RFC 5545 3.2.10
Leo Sunmo
committed
Updated printf's with proper verbs and removed extra %s
Leo Sunmo
committed
Add test for summary language
Leo Sunmo
committed

Commits on Apr 24, 2019

Commits on Aug 8, 2019

Add support for DATE-TIME values and email attendees (#25)

Michal Matyjek
authored and
PuloV
committed