DRYed it up a bit. Replaced '-' for '_' for class names.

[mauro-oto]

Hey @nicklink483

I opened this PR because I was having some trouble when I ran dare new game-1, which led to having a class named Game-1, which is not a valid class name. However, I'm not certain that this is a good solution, as there are plenty other cases. We should probably just edit the Readme and warn users to try to avoid special characters in the game name.

I also moved the normalized class name method to a separate method.

Please check it out, thanks!