Add PubSubHubbub hub urls as feed element

Add PubSubHubbub hub urls as feed element

Conflicts:
	spec/feedzirra/parser/atom_feed_burner_spec.rb
	spec/feedzirra/parser/atom_spec.rb
	spec/feedzirra/parser/rss_feed_burner_spec.rb
	spec/feedzirra/parser/rss_spec.rb