Add SSL support, switch to CircleCI

* Add SSL/TLS support for connecting to Docker instances over HTTPS.

* Switch from TravisCI to CircleCI since testing the SSL stuff on TravisCI just wasn't working out.

* Fix a bug where the HostConfig when starting containers would be ignored with Docker 1.2.0. Note that as part of this fix, we now have `ContainerInfo.hostConfig()` for getting the effective `HostConfig` by inspecting a container. This fixes #48.