Add mod documentation in seven languages

tests/ProjectionTests.cs

@@ -0,0 +1,27 @@
+namespace Cthangover.Mods.TileTopdown.Tests
+{
+    using Cthangover.Core.Mods.Testing;
+    using Godot;
+    /// <summary>Ground projection is invertible in every quadrant, before rounding to cells.</summary>
+    public class ProjectionTests
+    {
+        [ModTest("projection/ground_roundtrip_and_elevation")]
+        static void GroundRoundtrip(ModTestContext ctx)
+        {
+            var projection = new SquareTileProjection(32);
+            for (var y = -4; y <= 4; y++)
+            for (var x = -4; x <= 4; x++)
+            {
+                var point = new Vector2(x + 0.25f, y + 0.75f);
+                var pixel = projection.Project(new Vector3(point.X, point.Y, 0));
+                ModAssert.True(projection.Unproject(pixel).IsEqualApprox(point), "ground inverse including negative coordinates");
+            }
+            var ground = projection.Project(new Vector3(2, 3, 0));
+            var above = projection.Project(new Vector3(2, 3, 1));
+            ModAssert.CloseTo(32, ground.Y - above.Y, what: "one cell elevation");
+            ModAssert.CloseTo(32, projection.Unit, what: "projection pixel scale");
+            for (var direction = 0; direction < 4; direction++)
+                ModAssert.True(projection.CharsetRow(direction) >= 0 && projection.CharsetRow(direction) < 4, "valid facing row");
+        }
+    }
+}