Move the global variables to Terminal

[easeway]

This is cool piece. It will great if the following global variables can be moved to Terminal struct:

var (
    InputFD int       = unix.Stdin
    Input   io.Reader = os.Stdin
    Output  io.Writer = os.Stdout
)

I'm running this library with a few off screen terminal emulators, global variables doesn't work for me.

[easeway]

I can help refactoring the code if you don't have time to do that.