static public function php($dir,$args=[]) Very quickly deliver a php file by appending the url to a directory
Request url must end with a forward slash /
GET params are removed from url .. is removed from url
static public function file($dir, $url=null, $path_append'') Very quickly deliver a file. Supports browser caching.
Uses a very fast implementation for getting mimetypes. Each file extension has a *.txt file that contains its mimetype.
static public function set_download_file_name($file_name) Set the file name via headers.
Literally header("Content-Disposition: filename=\"$file_name\"", false);
static public function send_file($file_path, $path_append='') send headers & output file