This method receives the name of a static file that is going to be served
up and generates a dict of options to use when serving the file. The
default set is empty so code will fall back to the existing behavior if
the method is not overridden.
I needed this method to adjust the cache control headers for .js files that
one of my applications was statically serving. The default expiration is
buried in an argument to send_file and is set to 12 hours. There was no
good way to adjust this value previously.