0.3 - Skill tree, progression, and bug fixes

New skill tree feature!

- Play rounds and earn coins

- Spend earned coins on upgrades in the skill tree

- Balancing issues fixed! medium mode is now way more possible

- Playing different difficulties gets you a different amount of coins

- Quests can now be claimed to earn coins 

- Added a local leaderboard (in progress)

Playing the game now feels way more rewarding as you get stronger and can get further. Plans on adding more waves and bosses next!

Some bugs fixed:

- game crashing on death

- beating a wave made you restart on the next wave

- bullets dissapearing

- And more