Option to let Fresh respect X-Forwarded-* headers?

[dahlia]

I'd like to run Fresh behind a reverse proxy for both development and production. However, currently Fresh does not respect X-Forwarded-* headers, so when I try to get ctx.url it returns an http:// URL instead of https:// URL even though an X-Forwarded-Proto: https header is provided.

So, it would be nice if App.listen() has an option to let Fresh respect X-Forwarded-Proto and X-Forwarded-Host headers. Would it be a good idea? If so, I'd like to send a pull request.