Serve individual files in tar archives though web server

We store our build artifacts (test results, custom uploads) in tar.gz archives. It would be very convenient if our web server could serve individual files of these archives, so that we can link to them from e.g. the coin UI, and the user can view them in the browser, instead of having to download and extract files on their local machines.

E.g. `coin/artifacts/testresults.tar.gz?file=some/path.txt` would be served a (gzip compressed) text