I'd like to add a new functionality to an existing awaitable class by subclassing it.

Let's start with a very simple base class creating objects which asynchronously return 99 after a short sleep. The subclass should just add +1 to the result.

I can't find the proper way to use `super()` to refer to the base class.

```
import asyncio

class R99:
    def __await__(self):
        loop = asyncio.get_event_loop()
        fut = loop.create_future()
        loop.call_later(0.5, fut.set_result, 99)
        return fut.__await__()

class R100(R99):
    async def add1(self):
        v = await R99()
        #v = await super().__await__()   # <== error
        return v + 1

    def __await__(self):
        return self.add1().__await__()

async def test():
    print(await R99())
    print(await R100())

asyncio.get_event_loop().run_until_complete(test())

```