Added ability to change A-star cost function

scene/scene_string_names.cpp

@@ -32,6 +32,9 @@ SceneStringNames *SceneStringNames::singleton = NULL;
 
 SceneStringNames::SceneStringNames() {
 
+	_estimate_cost = StaticCString::create("_estimate_cost");
+	_compute_cost = StaticCString::create("_compute_cost");
+
 	resized = StaticCString::create("resized");
 	dot = StaticCString::create(".");
 	doubledot = StaticCString::create("..");

scene/scene_string_names.h

@@ -49,6 +49,9 @@ class SceneStringNames {
 public:
 	_FORCE_INLINE_ static SceneStringNames *get_singleton() { return singleton; }
 
+	StringName _estimate_cost;
+	StringName _compute_cost;
+
 	StringName resized;
 	StringName dot;
 	StringName doubledot;