CNBC: It’s been about a year since Twitter launched tests of e-commerce, and now it’s rolling out a “buy now” button system wide — so any U.S. retailer big or small can sell physical products, digital goods or services all within a tweet. Twitter says the move puts it on its way of being the world’s biggest social marketplace. The company is looking to make it easy for a wide range of retailers to come on board by integrating with all the major e-commerce platforms.