Associate state update logic with FSM states

[zsisco]

Want more expressive state update logic. Generate circuits (not just value output).

For example:

                                                "!stop"
                                                 .~~~.       
  .+---------.     "go"        .-----------------+.  !       
  |"acc':= 0"+~~~~~~~~~~~~~~~~>|"acc':= acc + val"|  !
  `----------'                 `-------+----------'<-'       
       ^                               !
       !                               ! 
"reset"!        .------------.         !"stop" 
       `~~~~~~~~+"acc':= acc"|<~~~~~~~~'  
                `------------'

So, some way to associate how external state acc gets updated according to the FSM state.