Build 28 & 29: things will get harder

I did this update live on stream, the VOD will be up soon. What’s new:

• ramped up difficulty (more enemies can spawn as more artifacts are picked up)
• artifact pickup gives health bonus + 5 seconds of invincibility (suggested by FlaviusKid - thanks!)
• when entering a new area, enemies won’t immediately attack you (they have to run their attack cooldown timer first)
• slightly randomized enemy rate of fire
• added a loading screen
• added a preliminary “skybox”
• time spent is now displayed on the game over screen