Use google.golang.org/protobuf instead of github.com/gogo/protobuf

This change replaces github.com/gogo/protobuf with
google.golang.org/protobuf, except for the code generators.

All proto-encoded structs are now generated from .proto files,
which include ttrpc.Request and ttrpc.Response.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

example/example_ttrpc.pb.go

@@ -0,0 +1,57 @@
+// Code generated by protoc-gen-go-ttrpc. DO NOT EDIT.
+// source: github.com/containerd/ttrpc/example/example.proto
+package example
+
+import (
+	context "context"
+	ttrpc "github.com/containerd/ttrpc"
+	empty "github.com/golang/protobuf/ptypes/empty"
+)
+
+type ExampleService interface {
+	Method1(ctx context.Context, req *Method1Request) (*Method1Response, error)
+	Method2(ctx context.Context, req *Method1Request) (*empty.Empty, error)
+}
+
+func RegisterExampleService(srv *ttrpc.Server, svc ExampleService) {
+	srv.Register("ttrpc.example.v1.Example", map[string]ttrpc.Method{
+		"Method1": func(ctx context.Context, unmarshal func(interface{}) error) (interface{}, error) {
+			var req Method1Request
+			if err := unmarshal(&req); err != nil {
+				return nil, err
+			}
+			return svc.Method1(ctx, &req)
+		},
+		"Method2": func(ctx context.Context, unmarshal func(interface{}) error) (interface{}, error) {
+			var req Method1Request
+			if err := unmarshal(&req); err != nil {
+				return nil, err
+			}
+			return svc.Method2(ctx, &req)
+		},
+	})
+}
+
+type exampleClient struct {
+	client *ttrpc.Client
+}
+
+func NewExampleClient(client *ttrpc.Client) ExampleService {
+	return &exampleClient{
+		client: client,
+	}
+}
+func (c *exampleClient) Method1(ctx context.Context, req *Method1Request) (*Method1Response, error) {
+	var resp Method1Response
+	if err := c.client.Call(ctx, "ttrpc.example.v1.Example", "Method1", req, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+func (c *exampleClient) Method2(ctx context.Context, req *Method1Request) (*empty.Empty, error) {
+	var resp empty.Empty
+	if err := c.client.Call(ctx, "ttrpc.example.v1.Example", "Method2", req, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}