publish Eventbrite events #275

Since FB API doesn't support event publishing (See #274 ) perhaps make it possible to publish Eventbrite events as another POSSE destination.

People in general seem to respond well to Eventbrite invitations, so this may solve some of the same use-case(s) as POSSE event to FB.

https://www.eventbrite.com/developer/v3/endpoints/events/#ebapi-post-events

Rough idea of how data could be copied from an indie event:
title: h-event p-name
description: h-event p-description
start_date: h-event dt-start
end_date: h-event dt-end
timezone: extract from h-event dt-start, or if none, then perhaps use https://github.com/esripdx/Timezone-API to extract timezone from location
privacy: 1 (presumably only public events for now)
personalized_url: perhaps convert the original event's URL to a URL-safe string for an event? e.g snarfed-org-event-1.eventbrite.com
venue_id: result of calling http://developer.eventbrite.com/doc/events/event_new/venue_new which should use the h-event's p-location h-card
organizer_id: result of calling http://developer.eventbrite.com/doc/events/event_new/organizer_new which should use the h-event's p-organizer h-card

I think those are the key fields, the rest we can incrementally figure out as we go.