Unify Markdown.output_foo methods to include the `raw` argument

[mnieber]

In my custom mistune.Renderer class I'm using the raw argument that is passed to the header function by Markdown.output_heading (it's the third argument in the call):

def output_heading(self):
    return self.renderer.header(
        self.inline(self.token['text']),
        self.token['level'],
        self.token['text']
    )

However, I also need it in output_paragraph. It would be nice if all the Markdown.output_foo methods pass the same arguments (where possible) when calling the methods of the renderer,