Revisit waitgroup (#241)

* Fix Add to waitgroup out of goroutines calling wg.Done()
* Pass waitgroup to other loop functions

internal/tinyproxy/loop.go

@@ -89,7 +89,6 @@ func (l *looper) Start()   { l.start <- struct{}{} }
 func (l *looper) Stop()    { l.stop <- struct{}{} }
 
 func (l *looper) Run(ctx context.Context, wg *sync.WaitGroup) {
-	wg.Add(1)
 	defer wg.Done()
 	waitForStart := true
 	for waitForStart {