fn new() FTP
fn (mut zftp FTP) connect(ip string) ?bool
fn (mut zftp FTP) login(user string, passwd string) ?bool
fn (mut zftp FTP) close() ?
fn (mut zftp FTP) pwd() ?string
fn (mut zftp FTP) cd(dir string) ?
fn (mut zftp FTP) dir() ?[]string
fn (mut zftp FTP) get(file string) ?[]byte