aio support

[sagewe]

any plan to introduce aio support?

I have modify servel line to deal with aio.Server typing in add_XXXServicer_to_server stub to workround in my project.
see fork

the code snippet used in my project is something like this:

from grpc import aio

server = aio.server()
demo_pb2_grpc.add_DemoServicer_to_server(..., server)

This modification works in grpc version with aio support only. I have no idea about how to generate stub works in situation where some hint types may not be available. Other choice is introduce a flag to generate feature specified stub.