Added aerodynamic drag

src/main/java/io/github/teampropulsive/physics/Aero.kt

@@ -0,0 +1,16 @@
+package io.github.teampropulsive.physics
+
+import io.github.teampropulsive.types.AtmoCompositionGas
+import net.minecraft.util.math.Vec3d
+
+class Aero {
+    fun calculate_aero(velocity : Vec3d, drag_coefficient : Double, area_in_direction : Double, atmo : ArrayList<AtmoCompositionGas>): Vec3d {
+        var average_density = 0.0;
+        for (gas in atmo) {
+            average_density += gas.gas.density * gas.quantity
+        }
+        average_density /= atmo.size.toDouble()
+        val force = velocity.multiply(velocity).multiply(average_density).multiply(0.5).multiply(drag_coefficient).multiply(area_in_direction)
+        return force
+    }
+}