Initial version of libcontainer API.

Docker-DCO-1.1-Signed-off-by: Victor Marmol <vmarmol@google.com> (github: vmarmol)

This is an initial proposal of what a libcontainer API would look like. You can see it is in no way implemented :) This is primarily for discussion on the API, we can merge this and start working on the individual pieces one at a time.

The proposed API borrows heavily from lmctfy and libct with some changes to improve on those. Key aspects are:
- Container names as hierarchical path
- Separating Creating a container from Getting a container (the latter gets a reference to a running container)
- Containers as objects we can perform action on.

Any and all comments are welcomed :) I think the documentation on these may be a little lighter than I'd like. I can add more as it is requested.
It would be nice to try to keep a lot of the rootfs logic out of libconatiner.  It's pretty nice that you can drop into any rootfs and just run a container there with a specific configuration.

The hard part is the steps where we need to populate dev or setup a tty for the container because any mounts that we want should happen inside the container's mount namespace before we start setting things up.  How much of these things can we move to the create phase?