A fast-growing e-commerce services provider is moving its headquarters from Houston to Austin. Cart.com employs 150 people in Austin, and executives say their plans call for at least 150 more local hires in the year ahead. The company got its start in Houston just over a year ago, and competes with Amazon and other e-commerce platforms. Cart-dot-com has created software and services it says will provide all the commerce functions necessary to grow a business online.