text: Title: [PR] Fix Windows Compatibility
  Body: > <a href="https://github.com/damc-dev"><img align="left" height="50" src="https://avatars0.githubusercontent.com/u/3859789?v=4"></a>        A pull request by [damc-dev](https://github.com/damc-dev) at _2019-11-06 01:44:29+00:00_
  > Original URL: https://github.com/zalando-incubator/kopf/pull/220
  > Merged by [nolar](https://github.com/nolar) at _2019-11-12 10:30:08+00:00_
  
  When running kopf on Windows it fails due to NotImplementedError thrown by add_signal_handler method in asyncio
  
  > Issue : #219 
  
  # Description
  In the asyncio docs it appears that the [add_signal_handler](https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.add_signal_handler) method is only available in Unix which is why it throws a NotImplementedError when kopf is run on Windows.
  This PR should fix Windows compatibility by catching NotImplementedError thrown by asyncio and continuing.
  
  # Types of Changes
  * Bug fix (non-breaking change which fixes an issue)
  
  ---
  
  > <a href="https://github.com/nolar"><img align="left" height="30" src="https://avatars0.githubusercontent.com/u/544296?v=4"></a>            Commented by [nolar](https://github.com/nolar) at _2019-11-13 18:25:01+00:00_
  > &nbsp;
  
  Released as [`kopf==0.23rc1`](https://github.com/nolar/kopf/releases/tag/0.23rc1).
  
  [damc-dev](https://github.com/damc-dev) Thank you for you contribution! 😉 