Implement 'wiki mode' - allows a site to be built based on templates alone.

Basically, this just allows you to say that an action is going to
specify a template that might not exist, and if it doesn't, please just
404 rather than crashing everywhere.

Then your site could have an action like this:

@blueprint.route('/', defaults={'path': '__homepage__'})
@blueprint.route('/<path:path>')
@render_html()
def index(path=None):
    return dict(
        _template = path,
        _wiki     = True,
    )

Resulting in a "wiki" built on jinja templates.