Add build command

spec/command_spec.cr

@@ -15,4 +15,22 @@ describe Game::Command do
     tile = world.map.get point
     tile.should be_a(Game::BuildingTile)
   end
+
+  it "should restrict build if not enought resources" do
+    world = Game::World.new create_map_2x2
+    point = Game::Point.new 1, 0
+    building = Game::Building.new Game::Building::Type::StartPoint, "Dummy", **{
+      construction: Game::Construction.new(
+        ts: 10,
+        cost: Game::Resources.new({
+          Game::Resources::Type::Crystals => 100,
+        }),
+        requirements: [] of Game::Building::Type
+      ),
+    }
+    command = Game::BuildCommand.new point, building
+    expect_raises(Game::NotEnoughtResources) do
+      world.push(command)
+    end
+  end
 end