Add return of new cell state to advanceState Function

lib/src/Cell.dart

@@ -11,11 +11,15 @@ class Cell {
 
   Cell([bool state = false]) : this.state = state;
 
-  void advanceState() {
+  // Sets the actual state to what it should be next update
+  // Returns the newly assumed actual state of the cell.
+  bool advanceState() {
     this.state = this.nextState;
     this.nextState = false;
 
     this.dirty = true;
+
+    return this.state;
   }
 
   void update(int neighbors) {