add event support

[zhangxuelai]

add event support

for example

conn, err := grpc.Dial("127.0.0.1:37101", grpc.WithInsecure(), grpc.WithMaxMsgSize(64<<20-1))
    if err != nil {
        fmt.Println(err.Error())
    }

    eventClient := pb.NewEventServiceClient(conn)
    filter := &pb.BlockFilter{
        Bcname: "xuper",
    }

    buf, _ := proto.Marshal(filter)
    request := &pb.SubscribeRequest{
        Type:   pb.SubscribeType_BLOCK,
        Filter: buf,
    }

    stream, err := eventClient.Subscribe(context.Background(), request)
    if err != nil {
        fmt.Print(err.Error())
    }

    for {
        event, err := stream.Recv()
        if err == io.EOF {
            fmt.Print(err.Error())
        }

        if err != nil {
            fmt.Print(err.Error())
        }
        fmt.Print(string(event.Payload))   
 }

[zhangxuelai]

@qizheng09

[zhangxuelai]

@yucaowang

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