Update 0.2.0

Hey all! This is mainly a quality-of-life update with some minor bug fixes and tweaks.
The next planned update will focus on adding new upgrades to the game.

• Gameplay
  • Fixed an issue where enemies wouldn't knock themselves back after hitting the player if they were grouped in a blob.
• Upgrades
  • Upgrades now show how many of that type have already been selected.
  • The pause menu and end-screen display a list of upgrades the player already owns. Click them to show upgrade details.
  • Fixed an issue where the wrong upgrade could be added when selecting multiple level-up upgrades.
  • Updated some upgrade icons.
• Parts
  • Fixed stinger turret projectiles not properly increasing in speed from upgrades.
  • Updated some part descriptions.
• Audio
  • Added new main menu music courtesy of my friend Nell! You can find her at the following links:
    • https://bsky.app/profile/arcturuscrane.bsky.social 
    • https://youtube.com/@eleanorcerar6273?si=c2a09VbIR0DTw_EE
  • Added a check to prevent the same sound from playing multiple times during the same frame from different sources (i.e. explosions).