have a cancel option when selecting squares.

After starting to select squares, upon realizing that I miscounted, or something, I'd like to be able to cancel my action. Currently it's not possible to stop entering selections without causing an error and requiring me to cancel the entire game and start over from the beginning. As a possibility: if, before I take my finger off the mouse, I pressed the key, and then, everything I did while the mouse button was pressed down would be ignored. It's very easy to be looking at the wrong column or row when counting or entering selections. It also would be useful to highlight the numbers--as well as the columns and rows. This is the number one problem I have with these sorts of games--after straining my eyes and counting blocks for many minutes, to be forced to start over when I really want to stop doing what I just started.