Correct ctypes definition of grantpt and ptsname
Update the constants in the pty module
Add a convenience function for fully setting up a pty
Use the pty setup convenience function
Go back to the separate fork and exec calls

This is much more amenable to changing file descriptors etc.
Setup the file descriptors in the child before exec
Actually implement sending outputs to the subprocess
Add example script files from demonstrate.sh
Handle the EOF case from stdin better
Close the master pty file descriptor in the child
Use is_empty instead of length = 0
Use the pseudo-terminal for all three std streams of child
Make the child just do a simple echoing with prefix