Memory leak in event loop inside a thread?

[darkestpigeon]

Another piece of info: replacing `std/asyncdispatch` with `chronos` fixes the 
problem in this case. But the problem returns with the following changes:
    
    
    proc cycler(x: ref MyObj) {.async.} =
      while true:
        x.value[] += 1
        echo x.value[]
        await sleepAsync(200)
    
    proc main_async() {.async.} =
      let x = new(MyObj)
      x[] = newMyObj(3)
      let fut = cycler(x)
      await sleepAsync(1000)
    
    
    Run

In this case, the `cycler` coroutine is still pending when the main coroutine 
(and the thread) finish. So there are still problems with clean-up on thread 
termination.