Assignment6 - Html renderer submission

I wonder, does it seem proper to you that the `append` method of this class should contain code that *renders* the thing to be appended?  Doesn't that seem a bit off?  

Methods should be atomic, meaning they do only one thing.  This method does two things.  It adds an item to the list of items *inside* this one, and if that item is renderable, it renders it.  

Much of what is problematic with the rest of your code stems from this choice here.