Example gRPC server and client with OpenCensus

This example uses:

gRPC to create an RPC server and client.
The OpenCensus gRPC plugin to instrument the RPC server and client.
Debugging exporters to print stats and traces to stdout.
```
$ go get go.opencensus.io/examples/grpc/...
```

First, run the server:

$ go run $(go env GOPATH)/src/go.opencensus.io/examples/grpc/helloworld_server/main.go

Then, run the client:

$ go run $(go env GOPATH)/src/go.opencensus.io/examples/grpc/helloworld_client/main.go

You will see traces and stats exported on the stdout. You can use one of the exporters to upload collected data to the backend of your choice.

You can also see the z-pages provided from the server: