async methods for Qset operations

I love using this library, and think it would be awesome to have an async way to perform get/updates,

e.g. Foo.objects.get, .filter, .save
is sync, and when we want to fetch many objects at once, it's better not to block the event loop

thinking of usage something like the below:
await Foo.aget_async(... OR await Foo.objects.aget_async(...
await Foo.afilter(...
await Foo.asave(...