Added prompt().

  This allows lua-scripts to prompt for input, via the user-interface.
  We can evaluate lua from the user-interface.

  Press ":" at the console and a prompt will appear, evaluating
 any lua you enter.
  Bind the "prompt" function.

      f = prompt( "enter your name: " )
  In the exit() function cleanup curses.

  TODO: Run the hook for at-exit
  The lua exit() function calls on_exit.

  This means however you exit the binary we call the exit-hook.