update README
Don't use console.error with a non-critical websocket close
properly initialize towtruck when startTowTruck() is called more than once in a single page session (i.e., after closing and restarting)
Put in some minimal checking in codemirror replace/update code
Added a confirmation when closing chat and ending the session.  Prettied up the intro screen just a little, with a Continue and Cancel screen.  Invalidate the shareId when stopping the session