0.2.1 Hotfix

Hotfix 

Little things:
--> Collision for the player in 1 player mode was turned off, it's now turned on
--> Particle effect for when you kill an invader was really small, fixed it
--> Changed the canvas from constant pixel size to scale with screen size

Things I forgot in the last devlog

Added a main menu
--> Main menu where you can choose between 1 player and 2 players modes
        It's going to be improved later on!

Little things:
--> changed start speed of the invaders
--> changed how many invaders spawn