Use hcalendar

I broke your scraper when I restructured eolclub.org ever so slightly. This PR fixes it, and also conveniently removes the Chronic dependency.

Supercedes PR #2.  I think this solution to the timezone issue (27de26c) is slightly preferable to the one from my previous attempt (21c7b7d).  Neither are great, but the previous one required manual conversion of the times in the sample content to UTC.

You can modify the timezone ruby works in by setting TZ in your shell before startup (e.g. set to "UTC" to simulate Travis' environment).  There doesn't seem to be a way to modify it once the interpreter is running, however.