Sorting feeds

[tsyesika]

Add the ability to sort feeds. This will mean every item needs to have a updated field (if one isn't provided use published value). Having the ability to to do

my_inbox = me.inbox[:100]
my_inbox.sort()

This would result in where my_inbox[0] would be the last updated item and my_inbox[-1] or my_inbox[99] would be the oldest object.