Create state

This replaces the pid and started files that are written in favor of one file serialized currently as json to record the container's state
I think we should be ok on the docker stuff.  Ppl know to build nsinit with the same tag as their docker version.  I made it clear up front for ppl that nsinit is a dev tool and we will break things.  

As far as libcontainer dep, I have a note in the readme at the top saying that if you depend on libcontainer and as we work though the API you should tag your dep to a specific tag or git commit.  Do you think this is enough?