Add restart option to Fig.

__Hello!__

I simply find this project really good, and ended up needing the `restart` option (Related to #478).

Since Docker 1.2 there is a `restart` option on `docker run`ning containers to add restart policies. I think fig options should be able to set restart policies to it's orchestrated containers.
This PR adds the option in Fig.

Let me know if there it's all ok?