Fix special events in parking api

The scraperwiki service is either dead or at the very least flaky.
Hitting https://views.scraperwiki.com/run/madison_parking_special_events_api/? directly fails (at least at the moment) which causes the entire parking API to fail.

Swapped out use of scraperwiki with direct call to city parking-special
events page then used BeautifulSoup to parse html and derive expected
json. Obivously a service provided by the city itself would be ideal but alas...

I isolated my changes to a single method to limit side effects but it's probably worth changing the way the api handles errors at some point. Maybe a future pull request.

Why is a guy from Denver contributing to a Madison API? 

For fun mostly.  I've been working on a little parking m-site that uses this service. Nothing mission critical. Madison because my wife went to school there and keeps threatening to move back and I found the API while exploring the madison tech community.  Site is here: http://mad-parking.appspot.com/ - should work if this pull request is merged and deployed.