Html render Assignment for 12/17

Nick Becker's HTML Render assignment for 12/17
I think the `html_tag` attribute of each of these classes might better be expressed as a class attribute.  There's no reason that each individual paragraph tag instance, or anchor tag instance, or other element instance would require a separate copy of the html tag name.  It's a small detail in this case, but getting in the habit of thinking about where various attribute should live leads to careful coding.