[feature] Using `cbor2` to read streams asynchronously in an `asyncio` application

Hi,

I would like to use `cbor2` to read CBOR streams in the context of an `asyncio` application.

From what I see, it is not possible now. Is that right?

From looking at the code, it looks like one should do the `read()` function of `Decoder` async, and then propagate the changes; each

```
value = self.read(length)
```

becomes

```
value = await self.read(length)
```

So I suppose it is not a quick change to be done, as most things need to become asynchronous.

Regarding the C extension, I am not sure what would be involved.