(gomoku-click): Position on nearest square. Adapt keymap accordingly.

(gomoku-click): Position on nearest square.  Adapt keymap accordingly.
(gomoku-mouse-play): Use it to play nearest to mouse click.
(gomoku-terminate-game): Factorize messages.
(gomoku): Allow interactive passing of board size.  Don't make a fuss
about restarting a game that hasn't progressed.
(gomoku-offer-a-draw): Give user the choice it pretended to give.
(gomoku-point-x): Deleted function.
(gomoku-point-y, gomoku-point-square): Simplified because point is
always on a square.
(gomoku-goto-xy, gomoku-plot-square): Fix line count due to
intangible newlines.
(gomoku-init-display): Once again fairly fast due to minimization of
characters in buffer and text-property operations.  Cursor cannot be
be off a square.
(gomoku-display-statistics): Simplified equivalently.
(gomoku-winning-qtuple-beg, gomoku-winning-qtuple-end)
(gomoku-winning-qtuple-dx, gomoku-winning-qtuple-dy): Pseudo variables
only used for non-functional argument passing deleted.
(gomoku-cross-winning-qtuple): Accordingly deleted function and
(gomoku-check-filled-qtuple): Accordingly adapted.
(gomoku-cross-qtuple): Don't be confused by tabs.
(gomoku-move-down, gomoku-move-up): Simplified because point is always
on square.
(gomoku-beginning-of-line, gomoku-end-of-line): New commands necessary
because intangible newlines perverted these.