Implemented every features mentioned in the Bonus Features 4.

It took way longer than I wanted it to be beacuse I decided to make a VFX for the fissure, which was more difficult than I thought, but I was also too stubborn to not commit to an idea that I wanted to implement.

I didn't end up making the sound effects for rockets or the explosion VFX because I just want to move on at the moment.

Some other things I think should've been included are: wave number UI, better powerup indicator that displays which powerup is currently active, better boss design (currently they just take less knockback from the player band powerups), and others that I most likely forgot.