Pty mode code added so that sshd server can do remote echo, backspace
processing. etc and ssh.exe client does not have to do local echo. We
can enrich it in future for more features and allowing programs like
powershell to run interactive. Pty mode is central for interactive use
and will be built using Windows console instead of termios that
Linux/Unix uses.
Whether LF should be changed to CR-LF is determined by what the remote
sshd server wants. Sequences like ESC[20h is sent by sshd servers in pty
ANSI mode. Unix servers usually want LF and Windows servers CR-LF. Added
simple ANSI data check now for pty use in interactive mode. Need to
expand to simple ANSI engine in future for processing other ANSI
terminal attributes.