State machines example : echo-server

[elcritch]

Note, when using a `ref object` you'll need to be a bit careful sending it 
between threads. It's best to use ARC/ORC with `move`, and there's a few 
details to be careful on, but overall it's pretty easy.
    
    
    type
      WorkerMachine* = object of StageMachine
      WorkerMachineRef* = ref WorkerMachine
    
    
    Run