Improved support for Schema.org microdata.

 - Fixed startDate itemprop, must follow ISO-8601 format.
 - Added itemtype Organization in the sponsors section.
 - Added itemtype Event in the Events index.
 - Added UTF-8 encoding by default.
Added itemprop doorTime in the events layout.

 - Adjusted date format in _posts (ISO-8601)
removed leading zero from event time
Merge pull request #52 from open-city/pull_51

schema.org