'Coin Duel' Mode Added

The first of the two non-racing modes has now been implemented (multiplayer only, and thusly not on the web version). Rather than the single obstacle suggested by the 20 Games Challenge, I opted for multiple 'obstacles', increasing in number as time ticks away. I made these 'obstacles' coins since it seemed more interesting than a plain old square, and also because it made a slight bit more sense.

I also added visuals for the 'Ready?/Go!' at the start, as well as a marker for which car is yours (only relevant when there are multiple cars, but it plays even when there's only one because... why not?).

All that's left is to add in a 'Tag' game mode, and then this game will finally be complete, at which point I can move on to game 5. I have a feeling such a game mode might be a bit rough to implement; it relies on cars colliding with each other, and that's a fairly questionable portion of my code. Nonetheless, it'll happen. There will still be plenty I could do to continue working on this game afterword, like add even more tracks or refine how collision works, but that'll be a project for future-me to consider.