While the industry has been focused on who might acquire the 3,900-unit Speedway convenience-store chain from Marathon Oil, Lacrosse, Wis.-based Kwik Trip has agreed to buy family-owned Stop-N-Go Convenience Centers, a 36-store chain based in Madison, Wis. Stop-N-Go stores are located in southern Wisconsin and northern Illinois, and fit well into Kwik Trip’s current Midwestern…