Template rendering outside of web requests

[cmlenz]

It should be easier to render a Genshi template with the default data outside of the normal request handler @output()/render() cycle.

For example, the moderation module in Divan currently uses the following code to render a plain text email:

template = app.templates.load('moderation/notification.txt',
                              cls=NewTextTemplate)
body = template.generate(post=post, reaction=reaction,
                         abs_url=abs_url, path_to=path_to,
                         quote=quote).render()

Note how it needs to pass the data that is normally available by default. This should be a one or two liner, at most.