Meteor Impacts

[benjaminiserman]

I'd like to add meteorite impacts. Spec:

• There should be a configurable (default 1%) chance of a meteorite striking per turn.
• The meteor impact should strike a random tile.
• The meteor impact should lower the elevation of the impacted tile by 200m to 2000m (both values configurable).
  • For each meter of water covering the tile, the meteor impact's elevation impact should decrease by one meter.
• The meteor impact should replace the top stone layer with a meteorite stone layer.
• The meteor impact should cause the middle stone layer to metamorphize (shock metamorphism).
• There should be a new StonePlacementCondition called TimeSinceMeteorImpactBelow with a possible threshold range of [2, 20]