function Renderer() {

                    /**
                     * Renderer#rules -> Object
                     *
                     * Contains render rules for tokens. Can be updated and extended.
                     *
                     * ##### Example
                     *
                     * ```javascript
                     * var md = require('markdown-it')();
                     *
                     * md.renderer.rules.strong_open  = function () { return '<b>'; };
                     * md.renderer.rules.strong_close = function () { return '</b>'; };
                     *
                     * var result = md.renderInline(...);
                     * ```
                     *
                     * Each rule is called as independed static function with fixed signature:
                     *
                     * ```javascript
                     * function my_token_render(tokens, idx, options, env, renderer) {
                     *   // ...
                     *   return renderedHTML;
                     * }
                     * ```
                     *
                     * See [source code](https://github.com/markdown-it/markdown-it/blob/master/lib/renderer.js)
                     * for more details and examples.
                     **/
                    this.rules = assign({}, default_rules);
                }
Renderer.renderToken(tokens, idx, options) -> String
- tokens (Array): list of tokens
- idx (Numbed): token index to render
- options (Object): params of parser instance

Default token renderer. Can be overriden by custom function
in [[Renderer#rules]].