Leveling up and powerups update

Today's update introduces character upgrades and powerups that will allow you to leave your base at later nights and survive longer than before.

Here's the list of character upgrades:
- Movement speed
- Reloading speed
- Toughness
- Health regeneration
- Pickup range

And powersups that boost your character for a short duration:
- Invulnerability
- Fast reload
- Invisibility
- Speed boost
- Magnet

Have fun!