Color balancing and a how to play!

I’ve done a bit of color balancing to make things better visible (thanks for the feedback again!) and have also added a small how to play screen accessible from the menu, plus a tiny controls overlay that will pop up for a second at the start of the game and then fade out.

I hopefully have also made sure that a quite annoying game breaking bug cannot happen anymore - difficult to tell, as I have not been able to reproduce it properly, so if you happen to run into an issue where you’ve reached the end of the stage, killed everything visible on screen and the stage doesn’t clear, it’s still in there. Let’s hope that not.