Added another enemy type

I have added another robot to the game, this is a gold sprite so it suits the theme to have this be the reward enemy, I am also thinking of having a particular type of enemy that the player wants to avoid e.g. one which slows you down more than the generic enemies.

I have added a simple score display and tweaked the physics a little so that you should not be able to keep going forever, although the enemies will now keep spawning, albeit with decreased density as you get further along.

The score stays in between runs, as I want this to be the currency that you spend on upgrades in the shop between runs.

I also added some parameters for how much each enemy type slows you down, and the same for the ground, so that these can be used to change the difficulty, and also as the mechanic behind the purchasable upgrades.

I would like to have the yeti fly out of an igloo or some sort of cannon at the start of the round, this could be moving back and forth so that you need to launch at the right time to get the best launch angle.

I am thinking of making it so that if you manage to fly high enough, the yeti will smash down with an anime style effect, which could hit more enemies, performing this maneuver could also be the basis for a boss fight, if I get time to implement it towards the end of the development.

I am also thinking of adding random background objects like signs and ice blocks to add some interest and graphical variety, as i think the game still looks a little plain, I would like to have some enemies be flying enemies, and add background objects higher up on the screen, perhaps birds or something similar.