Add keyboard event listeners

examples/events/on-key.lisp

@@ -0,0 +1,22 @@
+; this demo shows how to use the key events.
+;
+(clear)
+;
+(defn draw-title 
+  () 
+  (fill 
+    (text 30 80 50 "press key") "grey" 2))
+;
+(defn show-letter 
+  (e) 
+  (a
+    (clear) 
+    (draw-title)
+    (fill 
+      (text 30 170 50 (concat e:key " — " e:type)) "orange" 2)))
+;
+(draw-title)
+;
+(on "key-down" show-letter)
+(on "key-up" show-letter)
+(on "key-press" show-letter)