consider css minified by the same rules as javascript

I'm a bit unsure about the function name as there wasn't anything similar to take my lead from.

It seemed wasteful to fully duplicate the minified_javascript function just to change the file extension.

The sudden inclusion of CSS detection turned my decidedly Perl project from 99% Perl to a CSS project that was 71% CSS and 28% Perl.  This corrects that.  There was no prior art for testing of generated file detection that I could find.