Timeout async context manager.
Useful in cases when you want to apply timeout logic around block
of code or in cases when asyncio.wait_for is not suitable. For example:
>>> async with asyncio.timeout(10): # 10 seconds timeout
... await long_running_task()
delay - value in seconds or None to disable timeout logic
long_running_task() is interrupted by raising asyncio.CancelledError,
the top-most affected timeout() context manager converts CancelledError
into TimeoutError.