Simplify example

Signed-off-by: Michael Leuschel <leuschel@uni-duesseldorf.de>

Button/button_def.mch

 MACHINE button_def
-// An example that uses the new feature to use VisB DEFINITIONS
+// An example that uses VisB DEFINITIONS instead of a JSON and SVG file
 DEFINITIONS 
-     "LibraryStrings.def";
   VISB_JSON_FILE == "";
   VISB_SVG_BOX == rec(height:200, width:240);
- VISB_SVG_OBJECTS == rec(svg_class:"circle", `id`:"button",
-    cx:"100",cy:"100", r:"80",
-    stroke:"black", `stroke-width`:"3");
+  VISB_SVG_OBJECTS == rec(`id`:"button", svg_class:"circle",
+     cx:"100",cy:"100", r:"80", stroke:"black", `stroke-width`:"3");
   VISB_SVG_UPDATES == rec(`id`:"button",
      fill: IF button=TRUE THEN "green" ELSE "red" END);
- VISB_SVG_HOVERS == rec(`id`:"button", stroke:"gray",
-   `stroke-width`:"5")
-VARIABLES
-  button
-INVARIANT
-  button:BOOL
-INITIALISATION
-  button := FALSE
+  VISB_SVG_HOVERS == rec(`id`:"button",
+     stroke:"gray", `stroke-width`:"5")
+VARIABLES button
+INVARIANT button:BOOL
+INITIALISATION button := FALSE
 OPERATIONS
-  press_button = PRE button=FALSE THEN
-    button:=TRUE
-  END;
   toggle_button = BEGIN
     button:= bool(button=FALSE)
-  END;
-  set_button(newVal) = PRE newVal:BOOL THEN
-     button := bool(newVal=TRUE)
   END
 END
\ No newline at end of file