This mirrors all the "events" in a Basecamp account onto a stream in Zulip
(default "basecamp"); it sets the topic as the calendar or project that the
event belongs to.
Unfortunately, Basecamp will not host hooks, and neither do we, so this script
is currently intended to be run by our customers, much like the Trello mirror.
(imported from commit 484bc12681a43cd01fe0189c072ab4230eb32c22)