Add python-pty payload

This payload delivers a reverse connecting PTY shell. Use a socat listener - socat file:`tty`,echo=0,raw tcp4-listen:$PORT or use the lovely @jtripper's listener/client he committed at https://raw.github.com/infodox/python-pty-shells/master/tcp_pty_shell_handler.py
Merge pull request #44 from infodox/master

Add python-pty payload