`Samurai` instead of `Stripe` here because docs were out of date. Samurai was the first payment processor we used. They disappeared when [GroupOn acquired them](http://blog.gittip.com/post/25565694263/how-not-to-get-acquired), at which point we switched to Stripe. Stripe asked us to leave soon after because, at the time, they didn't support marketplaces. That's when Balanced gave us this PR.