move all files to common/ to begin repo merge

common/async.go

@@ -0,0 +1,15 @@
+package common
+
+import "sync"
+
+func Parallel(tasks ...func()) {
+	var wg sync.WaitGroup
+	wg.Add(len(tasks))
+	for _, task := range tasks {
+		go func(task func()) {
+			task()
+			wg.Done()
+		}(task)
+	}
+	wg.Wait()
+}