JSON file with array of sets (or set with one field of arrays of sets with `--alias-file-is-set-not-a-list`, may be useful i.e. [Nix packaging](https://github.com/ivabus/nixos/blob/master/roles/server/urouter.nix)).
Each set contains 2 necessary elements and 1 optional.
- Necessary
-`uri` (string) - of url after host (e.g., `/`, `some/cool/path`, should not start with `/` (only for root))
-`alias` (set) - set of one field
-`url` (string) - redirect to url with HTTP 303 See Other
-`file` (string) - read file from path `--dir/file` where `--dir` is option (default: `.`, see `--help`) and respond with HTTP 200 OK with `content-type: text/plain`
-`text` (string) - plain text HTTP 200 OK with `content-type: text/plain`