Errors and Cancelletion code samples for grpc-ruby

The examples in this directory show use of grpc errors.

On the server side, errors are returned from service
implementations by raising a certain GRPC::BadStatus exception.

On the client side, GRPC errors get raised when either:
* the call completes (unary and client-streaming call types)
* the response Enumerable is iterated through (server-streaming and
bidi call types).

To run the examples here:

Start the server:

> ruby error_examples_server.rb

Then run the client:

> ruby error_examples_client.rb