finds the rss/atom feed in a given url
Usage:
$ python -m feedfinder.init https://www.bbc.co.uk/sport/football http://feeds.bbci.co.uk/sport/football/rss.xml
>>> import feedfinder
>>> feedfinder.feed('https://bbc.co.uk/sport/football')
http://feeds.bbci.co.uk/sport/football/rss.xml