Make interesting changes to the game

Alex,

I have created a new folder in this repo with a new version of your "Doodle Jump" game.  Go to the folder and play the game!  You will realise that as you play the game, the gravity increases.  The new version of your game is to show you one of many ways that you could improve your game.  To see what is actually going on, go to main.js in that new folder I created.  I have left some comments so you can see the changes that I made to the game.

Have fun experimenting with the code!

 - Donald

P.S.  To see more examples of potential changes that could be made to your game, go to http://donaldkellett.github.io/Iron-Man-Jump-Experiments