2017.3.7
    - Allow kwargs to be passed through `new_container` into `client.containers.run`
    - Add demo to show customer command
2017.3.6
    - Add docker API version as an optional parameter
2017.3.5
    - Add utility get_open_port() to make it easy to get an unused port for a new container
2017.3.4
    - Moved pg_ready() and session_scope() out of tests and into main, because they're useful.
