Implement fire and petrol bomb weapon

[trundlr]

The petrol bomb weapon will require fire, which is part of this issue.

• Implement fire, which has an old implementation on the pre-rewrite branch
  • Fire dances around and makes lots of little holes in the terrain
• Implement the petrol bomb weapon which also has an old implementation
  • Breaks on impact, spreads fire around
• Allow crates to be hit, give them a health. If they reach 0 they explode with fire