Before filters in child routers leak into the parent
```nim
import asyncdispatch, jester

settings:
  port = Port(9001)

router api:
  before:
    try:
      discard request.cookies["auth_token"]
    except:
      halt Http403, "permission denied"

routes:
  extend api, "/api"

  get "/":
    resp Http200, "hahaha it's is an laughter image"
```

When this code is running, you can never get to the message on `/` without having the `auth_token` cookie set. This was surprising, as I expected the before filter to only run on routes under `/api`.