Allow based on file extension
This was originally suggested by Vitaut in http://pluckeye.uservoice.com/forums/137031-general/suggestions/7936581-url-prefix-matching.
"A similar feature would be useful for me - filtering by file extension or filetype.
Often, files with types such as tar. and patch are reported as application/octet-stream. So I'd like to allow .patch or .tar (or something similar with pluckeye looking at magic numbers in the response contents) while denying the rest of octet-stream."