# Async magic methods in contextlib.closing

I think `__aenter__` and `__aexit__` methods should be added to `contextlib.closing`, so that we can use `contextlib.closing` in async code too.

For example:

```python3
class SomeAPI:
    ...

    async def request(self):
        pass

    async def close(self):
        await self.session.close()
        

async with closing(SomeAPI()) as api:
    response = await api.request()
    print(response)
```

Also these methods can be moved to another class (like `asyncclosing` along the lines of `asynccontextmanager`).