Add stripped UnityEngine

.gitignore

@@ -1,5 +1,3 @@
-tools/
-
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 ##
@@ -289,6 +287,5 @@ __pycache__/
 *.odx.cs
 *.xsd.cs
 
-# Unity libraries
-lib/UnityEngine.dll
-lib/UnityEngine.CoreModule.dll
+# Cake binaries
+tools/