Translate /tutorials/webcomponents/customelements/ into Simplified Chinese

About 4 months ago I translated the article into Chinese and posted on [my blog](http://forcefront.com/2013/custom-elements-defining-new-elements-in-html/). Yesterday I just realized that I could contribute the localized version back to **HTML5Rocks** and benefit more people, especially developers from China and/or Chinese speakers in other countries and areas.