Add sudo

[SmsS4]

This pr is for this issue: #21
You can now run sudo commands like this:

package main

import (
	"fmt"
	"log"
)

func main() {
	// Start new ssh connection with private key.
	auth, err := Key("/home/smss/.ssh/id_rsa", "")
	if err != nil {
		log.Fatal(err)
	}

	client, err := New("smss", "127.0.0.1", auth)
	if err != nil {
		log.Fatal(err)
	}

	// Defer closing the network connection.
	defer client.Close()
	client.SetPass("test_pass")
	out, err := client.Run("sudo ls /")

	if err != nil {
		log.Fatal(err)
	}

	// Get your output as []byte.
	fmt.Println(string(out))
}