Graphviz representation of state diagram

This isn't a code change, so I'm not sure if people are interested in reviewing it. If I don't hear anything by mid-day Monday, I'll go ahead and merge.

I reproduced @tabbott's graphviz representation of the state machine, and added notes that @amb43790 and I made.  I would like to update this document further with the additional states that I'm adding for #6.  The version I've committed should reflect how master works today.

Also, I created a docs directory and moved the client spec to there so the root of the repository doesn't become cluttered.