Redirects can no longer be used in error blocks
First, thanks for all your work on Jester! It's a very nice framework. 

It seems that it's no longer possible to use a redirect within an error block with `0.5.0`. With Jester `0.4.3`, this snippet compiles and works as expected:

```
import jester

router root:
  get "/":
    resp "hello world"

  error Http404:
    redirect "404.html"

proc main() =
  var jester = initJester(root)
  jester.serve()

when isMainModule:
  main()
```
With `0.5.0`, I get the following compilation error:
```
/home/reesmichael1/programs/scorecord/example.nim(4, 8) template/generic instantiation of `router` from here
/home/reesmichael1/.nimble/pkgs/jester-0.5.0/jester.nim(1331, 39) template/generic instantiation of `async` from here
/home/reesmichael1/programs/scorecord/example.nim(9, 14) template/generic instantiation of `redirect` from here
/home/reesmichael1/.nimble/pkgs/jester-0.5.0/jester.nim(592, 11) Error: undeclared identifier: 'allRoutes'
```
If I change the `redirect` to a `resp`, the sample successfully compiles.

I haven't dug into it enough to be certain, but it seems likely that this is due to the changes in #265. Adding `halt = false` to the redirect call makes no difference.