done adding export-collision functionality, including collision message, in functional core. Next: add imperative shell scaffolding

fcore/normal-mode.sml

@@ -363,6 +363,7 @@ struct
     | KEY_CTRL_S => CommonUpdate.getSaveSquaresMsg model
     | KEY_CTRL_L => CommonUpdate.getLoadSquaresMsg model
     | KEY_CTRL_E => CommonUpdate.getExportSquaresMsg model
+    | KEY_CTRL_C => CommonUpdate.getCollisionMsg model
     | USE_SQUARES {squares, canvasWidth, canvasHeight} =>
         useSquares (model, squares, canvasWidth, canvasHeight)
     | SQUARES_LOAD_ERROR => CommonUpdate.squaresLoadError model