Configure extensions.

    Args:
        app (Flask): initialized Flask app instance

def bind_extensions(app):
    """Configure extensions.

    Args:
        app (Flask): initialized Flask app instance
    """
    # bind plugin to app object
    app.db = app.config['PUZZLE_BACKEND']
    app.db.init_app(app)

    # bind bootstrap blueprints
    bootstrap.init_app(app)
    markdown(app)

    @app.template_filter('islist')
    def islist(object):
        return isinstance(object, (tuple, list))