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?


Perhaps an an example using `max_retry` should be added somewhere. Should a list of valid options be shown or, alternatively, a link to the right section of the Docker documentation that explains this feature?