Offer: AsyncTask replacement

[mice777]

I have created Kotlin replacement for Android's AsyncTask. It's well tested on few larger projects of mine, it works beautifully and would fit this library.

Example:

asyncTask({
  doSomething()
}){ result ->
  processResult(result)
}

It's cancelable, it has optional callbacks when it's done or canceled, it passes return value from async thread back to main thread.

If there is interest, I can create pull request with this functionality.