Refactor game and ground object generation.

No real functional improvements yet, just reorganizing to make
improvements easier.

game/version.py

@@ -0,0 +1,8 @@
+from pathlib import Path
+
+
+#: Current version of Liberation.
+VERSION = "2.2.0-preview"
+if Path("buildnumber").exists():
+    with open("buildnumber", "r") as file:
+        VERSION += f"-{file.readline()}"