If sync API is used in a running loop start a new loop in a separate thread

[jacobtomlinson]

Closes #41

Tweaked the async wrapping code originally taken from universalasync with an implementation from jupyter-core that starts a new loop on a separate thread if a loop is already running.

Now when using the sync API:

• If no loop is running it will run the coroutine with asyncio.run
• If a loop is already running (and paused because we are in a sync function) it will start a new thread with a new loop and run the coroutine there