GRPC example - rewrite using interceptor

[zifter]

It's better to use interceptor instead of old approach described in old example
I'm using suggested interceptor and it's working pretty good.

[cyberw]

Looks nice. Can you add a small note to the docs about how this approach differs from Rpc example? (Callback instead of wrapper)

Oh, and are you sure import grpc.experimental.gevent as grpc_gevent etc is no longer needed? Have you tested it with many concurrent users?

[zifter]

@cyberw thanks for review!
Generally speaking, it's the same wrapper pattern, but implemented natively in grpc library. A bit more information about grpc interceptors. It's definitely not a callback, because interceptors wraps the original request, and a set of interceptors become a chain during a method call. So, who is working with grpc should know that pattern.

I didn't remove import grpc.experimental.gevent as grpc_gevent, it's moved because of correct import order in python.

Yes, I have tested with many users locally, it's working.

[cyberw]

Ah, I misread. Looks nice now!