Implement TcpSync driver

@lightsofapollo: I've got tests passing with this implementation, but I could use your feedback. Is this what you had in mind with [bug 892261](https://bugzilla.mozilla.org/show_bug.cgi?id=892261)? I think there is still more cleanup to do--removing more `HttpProxy`-related code, but I'm not sure exactly how far I should go there. Also, this breaks code in the `playground/` directory, and I'm not sure if you want to continue supporting it or remove it out right.