Cutting short Koa's middleware cascade
Sorry, I seem to have got my wires crossed… How would I go about cancelling or cutting short Koa's middleware cascade for instance in case of a redirect? I currently store a flag in `ctx.state` and check it in each middleware but this seems like a waste of cpu time. There's got to be a intended, more elegant solution. Should I just `return;`?

```javascript
app.use(async (ctx, next) => {
   if (redirect) {
      ctx.redirect(url, 303);
     // Stop the entire process here.
   }

   // only handle if there's no redirect.
   await next();
});

app.use(async (ctx, next) => {
   // only handle if there's no redirect.
   await next();
});

app.use(async (ctx, next) => {
   // only handle if there's no redirect.
   await next();
});
```