protocol: add messages

protocol/hello.proto

-syntax = "proto2";
+syntax = "proto3";
 
 package hello;
 
 message Hello {
-  optional string name = 1;
+  string name = 1;
 }
 
 message Bye {
 }
+
+message ComputeFlops {
+  double flop_amount = 1;
+}
+
+message WhatYouWannaDo {
+}
+
+message Order {
+  oneof order {
+    Hello hello = 1;
+    Bye bye = 2;
+    ComputeFlops compute_flops = 3;
+  }
+}