MarkdownCell = function (options) {
        /**
         * Constructor
         *
         * Parameters:
         *  options: dictionary
         *      Dictionary of keyword arguments.
         *          events: $(Events) instance
         *          config: ConfigSection instance
         *          keyboard_manager: KeyboardManager instance
         *          notebook: Notebook instance
         */
        options = options || {};
        var config = utils.mergeopt(MarkdownCell, {});
        TextCell.apply(this, [$.extend({}, options, {config: config})]);

        this.class_config = new configmod.ConfigWithDefaults(options.config,
                                            {}, 'MarkdownCell');
        this.cell_type = 'markdown';
    }
Generate JSON from cell
@return {object} cell data serialised to json