Can't compile with threads enabled using nim-httpauth
I am using [nim-httpauth](https://github.com/FedericoCeratto/nim-httpauth) with Jester. If I try to compile with `--threads:on`, I get the following error:

```
/home/user/.nimble/pkgs/jester-0.4.3/jester.nim(1277, 9) Hint: Asynchronous route: match. [User]
/home/user/Projects/project/bin/project.nim(19, 1) template/generic instantiation of `routes` from here
/home/user/.nimble/pkgs/jester-0.4.3/jester.nim(1283, 35) template/generic instantiation of `async` from here
/home/user/.nimble/lib/pure/asyncmacro.nim(272, 31) Error: 'matchIter' is not GC-safe as it accesses 'auth' which is a global using GC'ed memory
```

Using their example code. I'm not sure which module is most responsible. I also posted an issue here: https://github.com/FedericoCeratto/nim-httpauth/issues/22 . I'm also posting it here because I saw that there's a possibly related todo: https://github.com/dom96/jester/issues/110

I'm also wondering your input on how to maximize performance and how necessary a caching web server like nginx is. I see that there are some supplementary modules like beast and whip but they don't look like drop-in replacements or augments for Jester. I do need all the features of Jester and of course best performance possible but I digress.