Create a new middleware function to serve files from within a given root directory. The file to serve will be determined by combining req.url with the provided root directory. When a file is not found, instead of sending a 404 response, this module will instead call next() to move on to the next middleware, allowing for stacking and fall-backs. Enable or disable accepting ranged requests, defaults to true. Disabling this will not send Accept-Ranges and ignore the contents of the Range request header.