Provide iCal Feed

Aside from an attendees list, one feature of meetup.com that our website doesn't have is a calendar feed. We could easily implement one, though. It's just a matter of adding a file [like this one](https://github.com/crtr0/seattlehacks/blob/9bf59ea98cbddc34373c4270c5fb74b585faa4e7/events.ics) to the repo.