LD51 - Every 10 Seconds A... Wave

Every 10 seconds a... wave Humanity has just discovered time travel. You have been tasked with travelling back in time to test the safety. Unfortunately, you are stuck and it appears you have angered the locals. Build up your barricades and fight to survive for as long as you possibly can. My submission for Ludum Dare 51. Theme: Every 10 seconds a... Code: https://github.com/zai11/LD51