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.
I think the undo approach is reasonable. If it works, you get atomic behaviour. If it fails, you can return an "undo failed" error with an embedded cause consisting of the error which provoked the undo. The spec for the "undo failed" error can say that the resultant state is undefined. However, it's not clear how a user can recover from this undefined state other than by restoring the host OS to an earlier syncpoint.