* lisp/play/landmark.el: Use lexical-binding and avoid `intangible'.
(landmark--last-pos): New var. (landmark--intangible-chars): New const. (landmark--intangible): New function. (landmark-mode, landmark-move): Use it. (landmark-mode): Remove properties. (landmark-plot-square, landmark-point-square, landmark-goto-xy) (landmark-cross-qtuple): Don't worry about `intangible' any more. (landmark-click, landmark-point-y): Same; and don't assume point-min==1. (landmark-init-display): Don't set `intangible' and `point-entered'. (square): Remove. Inline it instead. (landmark--distance): Rename from `distance'. (landmark-calc-distance-of-robot-from): Rename from calc-distance-of-robot-from. (landmark-calc-smell-internal): Rename from calc-smell-internal.
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