Extend functionality.

Add func CleanScreen (https://github.com/mephux/readline/blob/master/readline.go#L244)
Add func ForceUpdateDisplay (https://github.com/mephux/readline/blob/master/readline.go#L244)
Add func ReplaceLine (https://github.com/mephux/readline/blob/master/readline.go#L255)
Add func RefreshLine (https://github.com/mephux/readline/blob/master/readline.go#L260)