Allow apps in feed collections to be grouped.

r? @ngokevin @diox
Did I get the form right, @ngokevin?

Sent from my iPhone

> On Jun 11, 2014, at 20:58, Kevin Ngo <notifications@github.com> wrote:
> 
> In docs/api/topics/feed.rst:
> 
> > @@ -748,6 +752,47 @@ Feed collections are represented thusly:
> >      *string|null* - the permanent URL for this collection.
> >  
> >  
> > +.. _feed-collections-grouped:
> > +
> > +When creating or updating a feed collection, the ``apps`` parameter may take
> > +two forms:
> nice!
> 
> —
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