Major clean up and reorganization

- Upgraded to Godot 4
- Just remembered the basic principles are based on a tile editor, and dramatically simplified from there. Derp.
- New state machine and license display add-ons.
- Re-licensed under the GPL because Micropolis' assets aren't under a separate one.

addons/simple-state/templates/State/empty_state.gd

@@ -0,0 +1,33 @@
+# meta-default: true
+extends _BASE_
+
+
+# Called when the state is activated. (parents, then children)
+func _enter() -> void:
+	pass
+
+
+# Called after the state is activated. (children, then parents)
+func _after_enter() -> void:
+	pass
+
+
+# Called every physics frame (only when the state is active, of course). (parents, then children)
+func _update(delta: float) -> void:
+	pass
+
+
+# Called at the end of every physics frame. (children, then parents)
+func _after_update(delta: float) -> void:
+	pass
+
+
+# Called before the state is deactivated. (parents, then children)
+func _before_exit() -> void:
+	pass
+
+
+# Called when the state is deactivated. (children, then parents)
+func _exit() -> void:
+	pass
+