Add support for Podlove Simple Chapters (http://podlove.org/simple-chapters)

Implemented support for the extension of the Atom Syndication and RSS 2.0 file format with simple chapter information described in this specification:
http://podlove.org/simple-chapters/

Example:
    In [1]: import feedparser

    In [2]: feed = feedparser.parse('http://hoersuppe.de/vorcast/')

    In [3]: feed['entries'][0]['sc_chapters']
    Out[3]: 
    {'chapters': [{'start': u'00:00:12.000',
       'start_parsed': datetime.timedelta(0, 12),
       'title': u'Livekalender'},
      {'start': u'00:02:24.000',
       'start_parsed': datetime.timedelta(0, 144),
       'title': u'Podcatcher'}],
     'version': u'1.0'}