Filled out the extra details of the Unread, Liked and Archive folders

[mauricerkelly]

In my usage of InstapaperKit I've found that I was using the folders created by the class methods [IKFolder unreadFolder] and so on. However, unlike folders I've pulled down from Instapaper these folders had no names or position indicators. I've updated the class methods to provide these for myself and thought I would offer them up to you.