Merge remote-tracking branches 'mwitkow/bugfix/grpc-timeouts' and 'mikeatlas/remote-addr-context' into master

Also,
* Resolved conflicts
* Unified two proposed metadta names "RemoteAddr" and "X-Forwarded-For"
  into "X-Forwarded-For"
* Add error handlings
* Add more tests
* Replaced test values with the ones defined in RFC 5737

Author: yugui

README.md

@@ -204,7 +204,7 @@ More examples are available under `examples` directory.
 * Mapping streaming APIs to JSON streams
 * Mapping HTTP headers with `Grpc-Metadata-` prefix to gRPC metadata
 * Optionally emitting API definition for [Swagger](http://swagger.io).
-* Import path parameters compatible to protoc-gen-go.
+* Setting [gRPC timeouts](http://www.grpc.io/docs/guides/wire.html) through inbound HTTP `Grpc-Timeout` header.
 
 ### Want to support
 But not yet.

examples/examplepb/a_bit_of_everything.pb.go

@@ -123,4 +123,9 @@ service ABitOfEverythingService {
 			body: "*"
 		};
 	}
+	rpc Timeout(EmptyMessage) returns (EmptyMessage) {
+		option (google.api.http) = {
+			get: "/v2/example/timeout",
+		};
+	}
 }