add root MergeIn

pttodo/root.go

@@ -18,3 +18,21 @@ func (root *Root) MoveScheduledToTodo() {
 		}
 	}
 }
+
+func (root *Root) MergeIn(root2 Root) {
+	for _, listPair := range [][2]*[]Todo{
+		[2]*[]Todo{&root.Todo, &root2.Todo},
+		[2]*[]Todo{&root.Scheduled, &root2.Scheduled},
+		[2]*[]Todo{&root.Done, &root2.Done},
+	} {
+		for _, candidate := range *listPair[1] {
+			found := false
+			for i := range *listPair[0] {
+				found = found || ((*listPair[0])[i].Todo == candidate.Todo)
+			}
+			if !found {
+				*listPair[0] = append(*listPair[0], candidate)
+			}
+		}
+	}
+}