Added Meteor Stomp special move

I have added a special move to the game, if the player manages to bounce high enough the Yeti will smash down into the ground as an icy meteor, destroying any nearby enemies.

It is fairly satisfying to watch a bunch of enemies all get destroyed at once, but I think the sound effects for the Meteor Stomp do need some work.

I also added a few visual tweaks, such as a prompt to enter the store when you can afford any upgrades, and a 'best distance' indicator on the ground so that you can tell when you are hitting a new record distance.

The volume setting also now works, I am still yet to implement the saving of upgrades, and the 'reset data' function.