Atom & RSS improved support

[elf-pavlik]

i just wanted to fetch and RSS feed from https://kippt.com/elfpavlik/shareroulette/feed

and needed in my template to dig into items as

    @feedr.feeds.kippt.rss.channel[0].item

and it seams that Atom may take similar, non obvious digging, not sure at this moment how it could work in a nicer way :(