add kbhit()

[k-okada]

add kbhit function

kbhit() Checks the console for a keystroke. retuns keycode value if a key has been pressed immediately, otherwise it returns nil. Note that this does not work well on Emacs Shell mode, run EusLisp program from terminal shell.

see #30, euslisp/EusLisp#237

(dotimes (i 10)
  (setq c (kbhit))
  (if c
     (format t "~c(~d)~%" c c))
    (format t "no input...~%"))
  (unix::sleep 1))