Add sleep state to state machine, timeouts to the workers to prove concurrency

Now each run can have different orders:
```js
> concur()
undefined
20 + 40 + 70 = 130 
> concur()
40 + 20 + 70 = 130
> concur()
undefined
70 + 20 + 40 = 130
> concur()
20 + 40 + 70 = 130
```