* lisp/play/gomoku.el: Don't use intangible property. Use lexical-binding.

* lisp/play/gomoku.el: Don't use intangible property.  Use lexical-binding.
(gomoku--last-pos): New var.
(gomoku--intangible-chars): New const.
(gomoku--intangible): New function.
(gomoku-mode): Use it.  Derive from special-mode.
(gomoku-move-up): Adjust line count.
(gomoku-click, gomoku-point-y, gomoku-point-square, gomoku-goto-xy)
(gomoku-plot-square, gomoku-init-display, gomoku-cross-qtuple):
Simplify accordingly.