Support to deal with ctrl-z

[m9rco]

By the following，I want to close any out of the way the current session，But when the user use Ctrl -z will switch into the background

    shell.Interrupt(func(c *ishell.Context, count int, input string) {
      return
    })
    shell.EOF(func(c *ishell.Context) {
      return
    })

[m9rco]

#133 Fix the problem