In this update:

• Added a "vX.X" label on the main menu to show game version
• Optimised the particle system (and some code) to stop FPS drops when spamming cannon shots.
• Reduced the game from 15 levels to 10, and adjusted difficulty to make lvl10 as hard as lvl15 originally was

I would have left it as it was for the Major Game Jam, but it didn't occur to me that other people were suffering FPS drops where my beefy PC was seemingly ok. My bad!