Tons of fixes, upgrades and new features!

• Sandbox mode - do whatever you want! You’re immortal and have infinite everything
• New survivors acting, including watching around, better physics, more intelligent walking and more
• New mission task - dogfight
• Rewritten mountains generator - now generated landscapes looks better than the handmade in main scenario! Try it in random game mode.
• New cinematic camera
• Funny big headed survivors mode enabled by cheat code (read below)
• New cheat codes
• And much more! If you want to know all the changes, please look at my github and read the commit history: https://github.com/GadZombie/retrofire/activity