Added support for attributes on fenced code blocks, e.g., ```{.lang .class2 #id attr="value"} (thanks, @thothal, #106).

Fixed the bug that the option number_sections: true doesn't work for HTML output when then input contains certain Unicode characters (thanks, @fyuniv, #104).

Added support for rendering HTML Widgets such as ggplotly (thanks, @fyuniv, #105).