Some visual tweaks

I’ve made some mostly visual updates to the game, revamping the welcome page, the in-game HUD, and the game over screen. One entirely new feature is: distance! the game will track how far you travel during a run, in addition to how long you last.

Of course, in a 2d game distance is kind of imaginary– I decided to base the calculation on the assumption that the robot has approximately the diameter of a basketball.