gd,refacto: added state chart addon and namespace cleanup

addons/godot_state_charts/guard.gd

@@ -0,0 +1,13 @@
+@icon("guard.svg")
+class_name Guard
+extends Resource
+
+## Returns true if the guard is satisfied, false otherwise.
+func is_satisfied(context_transition:Transition, context_state:StateChartState) -> bool:
+	push_error("Guard.is_satisfied() is not implemented. Did you forget to override it?")
+	return false
+
+## Returns the triggers which should trigger the guard's evaluation. This is a bit mask of [StateChart.TriggerType].
+func get_supported_trigger_types() -> int:
+	push_error("Guard._get_supported_trigger_types() is not implemented. Did you forget to override it?")
+	return StateChart.TriggerType.NONE