Add tiled map, tilesheet configs etc

These are just XML so relatively git-friendly.  They're needed for the
game and should be syncronised to the version of the code so they
really ought to be checked in.

assets/game.tiled-project

@@ -0,0 +1,14 @@
+{
+    "automappingRulesFile": "",
+    "commands": [
+    ],
+    "compatibilityVersion": 1100,
+    "extensionsPath": "extensions",
+    "folders": [
+        "."
+    ],
+    "properties": [
+    ],
+    "propertyTypes": [
+    ]
+}