Fix a few documentation errors

There were a few places in the friends_and_followers.rb documentation where the same text - "Returns an array of numeric IDs for every user the authenticated user is following" - this snippet must have been copy/pasted from another method, but it actually is incorrect for the method it was listed with.  For example, the 'friends' method does not return only the IDs, but actually returns the full collection of user objects.  This patch corrects four such instances in the documentation.