announce: unofficial gRPC Guice scopes

[Piotr Morgwai Kotarbinski]

Hello all,

Recently I've finally found some time to polish and generalize a set of classes providing Guice scopes for gRPC, that I was copy-pasting-tweaking for every grpc-java project for the last few years: maybe someone else will find it useful :)

https://github.com/morgwai/grpc-scopes

it provides `rpcScope` and `listenerCallScope`. Oversimplifying, in case of a streaming client, `listenerCallScope` spans over processing of a single message from client's stream, while `rpcScope` spans over a whole given RPC. Oversimplifying again, in case of a unary client, these 2 scopes have roughly the same span.

Feedback is welcome :)

Cheers!