Enhancing current-month logic

So the month changing logic that we've set up here is a little incomplete, because it

seems to work until you get to January and then you try and decrement again and then

nothing seems to happen, because you can't; okay, so what's basically happening is we're

going this.month-1, and if it's already at not then we get -1, so yeah this seems to

have actually sort of crash the browser there, which is interesting.

Anyway, clearly we need to make a bit of change