Update: Adjusted graphics, warning screen, and new item pickup

Minor adjustments according to feedback.

First and foremost, a warning screen for the flashing images and bright colors has been added to the beginning. Additionally, in an attempt to mitigate the issue, the flashing numbers and the death bar at the bottom of the screen now switches between two slightly different shades of yellow, instead of the stark flashing on and off. The GO sprite also now has a scrolling animation instead of the letters alternating between red and green.

A different item has also been added. This one will decrease instead of increase their speed. The same item will always spawn for both players for the sake of balance. On top of being arrows pointing backward instead of forward, they'll also have the color scheme of the enemy player to make them more immediately distinguishable.

Thanks for the feedback. If anyone else would like more improvements, I'll try to implement them.