chaooo

in my case, i want to copy multiple file at a time, just like ```golang fun main() { ... client := scp.NewClient("example.com:22", &clientConfig) ... err := client.CopyFile(context.Background(), f1, "/tmp/1.txt", "0755")...

Has passed the test in the test environment. could you take a look, check again?

just like i want to count the number of ping，or set close the connection if there is no ping message whithin two cycle.