public function at_template(array $info, string $templateName, ...$templateArgs)
public function at_import(array $info, string $key) Import something previously exported with @export or @export_start/@export_end
public function at_file(array $info, string $relFilePath)
public function at_see_file(array $info, string $relFilePath)
public function at_hard_link(array $info, string $url, string $name=null) just returns a regular markdown link. In future, may check validity of link or do some kind of logging
public function at_easy_link(array $info, string $service, string $target)